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The goal of present study is to explore how the size and functionalization of graphene quantum dots (GQDs) affect their sensing capabilities. Specifically, we investigated the adsorption of SO2, SOF2, SO2F2, and SF6 on GQDs that were functionalized with -CH3, -COCH3, and -NH2. We used density functional theory to analyse the electronic properties of these functionalized GQDs and found that the functionalization significantly altered their electronic properties. For example, the B3LYP H-L gap of pristine triangulene was 3.9eV, while the H-L gap of functionalized triangulene ranged from 2.8 eV to 3.6 eV (using the B3LYP functional). Our results indicate that -NH2 functionalized phenalenyl and triangulene provide strong interaction with SO2, with adsorption energies of-0.429 eV and-0.427 eV, respectively. These adsorption properties exhibit phys-isorption, leading to high gas sensitivity and superior recovery time. The findings of this study provide new insights into the potential use of GQDs for detecting the decomposed constituents of sulfur hexafluoride, which can be beneficial for assessing the operation status of SF6 insulated devices. Overall, our calculations suggest that functionalized GQDs can be employed in gas insulated systems for partial discharge detection.

The geometry optimization of 30 paramagnetic defects, including biomedically attractive nitrogen-, silicon-, germanium-, and nickel-related color centers, is performed after their incorporation into hydrogenated nano -diamond (ND) of C84H64 size. The main aim is to examine the effectiveness of the low-cost methods, namely, PBEh-3c, r2SCAN-3c, B97-3c, HF-3c, and GFN2-xTB, in reproducing the geometries of these defects basing on the similarity between the results of the subsequent electronic g-tensor calculations. It is revealed that the overall performance of PBEh-3c, r2SCAN-3c, and B97-3c is very alike and can be considered as good, however, none of these "3c" approaches is able to cope with all tested geometries. The results of HF-3c, on the other hand, are disappointing, as this method is outperformed by computationally much more lighter GFN2-xTB. Additional calculations carried out for dangling bonds introduced into hydroxylated and aminated NDs show that all low-cost methods perform reasonably well for this type of defect but the largest quantitative discrepancies once again are demonstrated by HF-3c. The obtained findings lay the foundations for the future studies of larger NDs with the purpose to figure out the magnetic properties dependence on the size of NDs or defect positions within NDs., QC 20230630

Stacking fault energy and twinning stress are thought to be closely correlated. All currently available models predict a monotonous decrease in twinning stress with decreasing stacking fault energy and depart from the assumption that the intrinsic stacking fault energy has a positive value. Opposite to this prediction, for mediumand high-entropy alloys the twinning stress was shown to increase with decreasing SFE. Additionally, for metastable materials, first principles methods predict negative intrinsic stacking fault energy values, whilst experimentally determined values are always positive. In the present communication, it is postulated that the twinning stress scaled by the Burgers vector bridges the difference between intrinsic and experimentally measured stacking fault energy. The assumption is tested for Cu-Al alloys, for pure metals and for medium- and high-entropy alloys and, for the first time, provides a consistent quantitative interpretation of data for both alloys with positive and negative stacking fault energy., QC 20230503

The goal of present study is to explore how the size and functionalization of graphene quantum dots (GQDs) affect their sensing capabilities. Specifically, we investigated the adsorption of SO2, SOF2, SO2F2, and SF6 on GQDs that were functionalized with -CH3, -COCH3, and -NH2. We used density functional theory to analyse the electronic properties of these functionalized GQDs and found that the functionalization significantly altered their electronic properties. For example, the B3LYP H-L gap of pristine triangulene was 3.9eV, while the H-L gap of functionalized triangulene ranged from 2.8 eV to 3.6 eV (using the B3LYP functional). Our results indicate that -NH2 functionalized phenalenyl and triangulene provide strong interaction with SO2, with adsorption energies of-0.429 eV and-0.427 eV, respectively. These adsorption properties exhibit phys-isorption, leading to high gas sensitivity and superior recovery time. The findings of this study provide new insights into the potential use of GQDs for detecting the decomposed constituents of sulfur hexafluoride, which can be beneficial for assessing the operation status of SF6 insulated devices. Overall, our calculations suggest that functionalized GQDs can be employed in gas insulated systems for partial discharge detection.

The goal of present study is to explore how the size and functionalization of graphene quantum dots (GQDs) affect their sensing capabilities. Specifically, we investigated the adsorption of SO2, SOF2, SO2F2, and SF6 on GQDs that were functionalized with -CH3, -COCH3, and -NH2. We used density functional theory to analyse the electronic properties of these functionalized GQDs and found that the functionalization significantly altered their electronic properties. For example, the B3LYP H-L gap of pristine triangulene was 3.9eV, while the H-L gap of functionalized triangulene ranged from 2.8 eV to 3.6 eV (using the B3LYP functional). Our results indicate that -NH2 functionalized phenalenyl and triangulene provide strong interaction with SO2, with adsorption energies of-0.429 eV and-0.427 eV, respectively. These adsorption properties exhibit phys-isorption, leading to high gas sensitivity and superior recovery time. The findings of this study provide new insights into the potential use of GQDs for detecting the decomposed constituents of sulfur hexafluoride, which can be beneficial for assessing the operation status of SF6 insulated devices. Overall, our calculations suggest that functionalized GQDs can be employed in gas insulated systems for partial discharge detection.

The goal of present study is to explore how the size and functionalization of graphene quantum dots (GQDs) affect their sensing capabilities. Specifically, we investigated the adsorption of SO2, SOF2, SO2F2, and SF6 on GQDs that were functionalized with -CH3, -COCH3, and -NH2. We used density functional theory to analyse the electronic properties of these functionalized GQDs and found that the functionalization significantly altered their electronic properties. For example, the B3LYP H-L gap of pristine triangulene was 3.9eV, while the H-L gap of functionalized triangulene ranged from 2.8 eV to 3.6 eV (using the B3LYP functional). Our results indicate that -NH2 functionalized phenalenyl and triangulene provide strong interaction with SO2, with adsorption energies of-0.429 eV and-0.427 eV, respectively. These adsorption properties exhibit phys-isorption, leading to high gas sensitivity and superior recovery time. The findings of this study provide new insights into the potential use of GQDs for detecting the decomposed constituents of sulfur hexafluoride, which can be beneficial for assessing the operation status of SF6 insulated devices. Overall, our calculations suggest that functionalized GQDs can be employed in gas insulated systems for partial discharge detection.

The goal of present study is to explore how the size and functionalization of graphene quantum dots (GQDs) affect their sensing capabilities. Specifically, we investigated the adsorption of SO2, SOF2, SO2F2, and SF6 on GQDs that were functionalized with -CH3, -COCH3, and -NH2. We used density functional theory to analyse the electronic properties of these functionalized GQDs and found that the functionalization significantly altered their electronic properties. For example, the B3LYP H-L gap of pristine triangulene was 3.9eV, while the H-L gap of functionalized triangulene ranged from 2.8 eV to 3.6 eV (using the B3LYP functional). Our results indicate that -NH2 functionalized phenalenyl and triangulene provide strong interaction with SO2, with adsorption energies of-0.429 eV and-0.427 eV, respectively. These adsorption properties exhibit phys-isorption, leading to high gas sensitivity and superior recovery time. The findings of this study provide new insights into the potential use of GQDs for detecting the decomposed constituents of sulfur hexafluoride, which can be beneficial for assessing the operation status of SF6 insulated devices. Overall, our calculations suggest that functionalized GQDs can be employed in gas insulated systems for partial discharge detection.

Porphyrins constitute a class of attractive materials for harvesting sunlight and promote chemical reactions following their natural activity for the photosynthetic process in plants. In this work, we employ an in-silico design strategy to propose novel porphyrin-based materials as photocatalysts for hydrogen evolution reaction (HER). More specifically, a set of meso-substituted porphyrins with donor-acceptor architecture are evaluated within the density functional theory (DFT) framework, according to these screening criteria: i) broad absorption spectrum in the ultraviolet-visible (UV-Vis) and near infrared (NIR) range, ii) suitable redox potentials to drive the uphill reaction that lead to molecular hydrogen formation, iii) low exciton binding free energy (E-b), and iv) low hydrogen binding free energy (delta G(H)), a quantity that should present low HER overpotentials, ideally delta G(H) = 0. The outcomes indicate that the Se-containing compound, where the donor ligands are attached to the porphyrin core by the spacer, outstands as the most promising candidate that is presented in this work. It displays a broad absorption in the visible and NIR regions to up to 1000 nm, suitable catalytic power, low E-b (in special in high dielectric constant environment, such as water) and the lowest delta G(H) = +0.082 eV. This is comparable, in absolute values, to the value exhibited by platinum (delta G(H) =-0.10 eV), one of the most efficient catalysts for HER.

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1-delta OxN1-x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ~& nbsp;0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1-delta OxN1-x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1-delta OxN1-x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts. (C)& nbsp;2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.& nbsp

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al2OS as an efficient photocatalyst material for hydrogen-production H-2 through the first-principles calculations. Janus Al2OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al2OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al2OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al2OS, the absorption-coefficient of Janus Al2OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al2OS has been investigated. Our calculations demonstrate that the band edge position of Al2OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy Delta G(H*) of Al2OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga2XY (X, Y = S, Se, Te with X not equal Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/angstrom of an external electrical field. Our results indicate that Janus Al2OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1-delta OxN1-x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ~& nbsp;0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1-delta OxN1-x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1-delta OxN1-x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts. (C)& nbsp;2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.& nbsp

Porphyrins constitute a class of attractive materials for harvesting sunlight and promote chemical reactions following their natural activity for the photosynthetic process in plants. In this work, we employ an in-silico design strategy to propose novel porphyrin-based materials as photocatalysts for hydrogen evolution reaction (HER). More specifically, a set of meso-substituted porphyrins with donor-acceptor architecture are evaluated within the density functional theory (DFT) framework, according to these screening criteria: i) broad absorption spectrum in the ultraviolet-visible (UV-Vis) and near infrared (NIR) range, ii) suitable redox potentials to drive the uphill reaction that lead to molecular hydrogen formation, iii) low exciton binding free energy (E-b), and iv) low hydrogen binding free energy (delta G(H)), a quantity that should present low HER overpotentials, ideally delta G(H) = 0. The outcomes indicate that the Se-containing compound, where the donor ligands are attached to the porphyrin core by the spacer, outstands as the most promising candidate that is presented in this work. It displays a broad absorption in the visible and NIR regions to up to 1000 nm, suitable catalytic power, low E-b (in special in high dielectric constant environment, such as water) and the lowest delta G(H) = +0.082 eV. This is comparable, in absolute values, to the value exhibited by platinum (delta G(H) =-0.10 eV), one of the most efficient catalysts for HER.

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1-delta OxN1-x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ~& nbsp;0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1-delta OxN1-x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1-delta OxN1-x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts. (C)& nbsp;2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.& nbsp

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al2OS as an efficient photocatalyst material for hydrogen-production H-2 through the first-principles calculations. Janus Al2OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al2OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al2OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al2OS, the absorption-coefficient of Janus Al2OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al2OS has been investigated. Our calculations demonstrate that the band edge position of Al2OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy Delta G(H*) of Al2OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga2XY (X, Y = S, Se, Te with X not equal Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/angstrom of an external electrical field. Our results indicate that Janus Al2OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting

The effect of a series of triarylamine based D-pi-A organic dyes, namely RK1, BA504, BA741 and the simple L1 reference dye on solid-state dye sensitized solar cells (s-DSSCs) performances was studied. The solid hole transporting material (HTM) was obtained by in-situ photoelectrochemical polymerization (in-situ PEP) process applied in two different media (water and acetonitrile) to produce the poly-3,4 ethylenedioxythiophene (PEDOT) conducting polymer (CP). A joint experimental and theoretical (density functional theory and time-dependent density functional theory) study is conducted to correlate the dye molecular structure containing different donor, pi-bridge or acceptor with several physicochemical characteristics such as optical (absorption and emission), electronic and redox properties of dyes in organic and aqueous medium; in-situ PEP process and charge transfer kinetics at the DSSC interfaces (Dye/TiO2 and Dye/HTM) through the alignment of the different energy levels of the dyes and electrodes. These properties are considered since they govern the performance of s-DSSCs denoted by the short-circuit current (J(sc)), open circuit cell potential (V-oc) and fill factor (FF). Among the four studied dyes, the s-DSSCs based on RK1, shows the best power conversion efficiency of 1.75% resulting from highest FF (0.57), V-oc (550 mV) and J(sc) (5.6 mA/cm(2)). The large differences in experimental photovoltaic performances of the obtained s-DSSCs have been well outlined and provide the guidelines for future development of more efficient solar-cell sensitizers.

Porphyrins constitute a class of attractive materials for harvesting sunlight and promote chemical reactions following their natural activity for the photosynthetic process in plants. In this work, we employ an in-silico design strategy to propose novel porphyrin-based materials as photocatalysts for hydrogen evolution reaction (HER). More specifically, a set of meso-substituted porphyrins with donor-acceptor architecture are evaluated within the density functional theory (DFT) framework, according to these screening criteria: i) broad absorption spectrum in the ultraviolet-visible (UV-Vis) and near infrared (NIR) range, ii) suitable redox potentials to drive the uphill reaction that lead to molecular hydrogen formation, iii) low exciton binding free energy (E-b), and iv) low hydrogen binding free energy (delta G(H)), a quantity that should present low HER overpotentials, ideally delta G(H) = 0. The outcomes indicate that the Se-containing compound, where the donor ligands are attached to the porphyrin core by the spacer, outstands as the most promising candidate that is presented in this work. It displays a broad absorption in the visible and NIR regions to up to 1000 nm, suitable catalytic power, low E-b (in special in high dielectric constant environment, such as water) and the lowest delta G(H) = +0.082 eV. This is comparable, in absolute values, to the value exhibited by platinum (delta G(H) =-0.10 eV), one of the most efficient catalysts for HER.

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al2OS as an efficient photocatalyst material for hydrogen-production H-2 through the first-principles calculations. Janus Al2OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al2OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al2OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al2OS, the absorption-coefficient of Janus Al2OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al2OS has been investigated. Our calculations demonstrate that the band edge position of Al2OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy Delta G(H*) of Al2OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga2XY (X, Y = S, Se, Te with X not equal Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/angstrom of an external electrical field. Our results indicate that Janus Al2OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting

Diffusionless transformations allow access to metastable phases and enrich the materials design portfolio. They are well suited for atomistic modeling; nonetheless, they are challenging when involving disordered systems or alloys with complex compositions. This work presents a comprehensive study of transforma-tion energetics between bcc and hcp ordered and disordered phases in the TiAl+Mo model alloy system. By employing two complementary techniques I. VASP-SQS, and II. EMTO-CPA, we can show that chemical disorder flattens the energy landscape but may introduce a small barrier. Unlike that, the energetics of ordered phases are barrier-less and hence would suggest a spontaneous transformation. Finally, we show that Mo stabilizes the bcc phases, leading to a barrier-less transformation hcp -+ bcc for both ordered and disordered states when Mo content exceeds ti 12 at.%., QC 20221102

In this paper, the distribution characteristics of gas, liquid, and solid products of low-rank coal by hydrothermal carbonization (HTC) at different temperatures are studied. Advanced testing methods are used to explore changing rules of physicochemical characteristics. Reaction properties of different regions are explained based on the mechanism of quantum chemistry. Experimental results showed that as the temperature increases, the volatile content decreases, the fixed carbon content increases, and impurities are removed in the form of gas or ions. The coal aliphatic properties are reduced, whereas the aromatization degree is significantly enhanced. Meanwhile, the specific surface area after upgrading is reduced, but the average pore diameter is increased, and the pore structure density is enhanced. The content of carbon-containing groups increases but that of carbon-oxygen groups decreases, which corresponds to the O/C ratio. Theoretical calculation results demonstrate that the more negative and positive areas of the surface electrostatic potential (ESP), the smaller distribution proportion. The ESP value in the vicinity of oxygen-containing group is relatively negative, indicating that it is more reactive, which is a good proof of the experiment's conclusions. In summary, low-rank coal obtained after HTC meets the blast furnace injection requirements and can be used for injection., QC 20221026

Through density functional theory (DFT), we investigate the electronic and transport properties of zigzag phosphorene nanoribbons (ZPNRs) and armchair phosphorene nanoribbons (APNRs) passivated with only H or O, or both H and O with different arrangements, systematically. According to the calculated cohesive energies, all structures are stable. Also, the simulation results reveal a semiconductor-to-metal transition in zigzag groups, but all the APNRs are semiconductors. We see the direct-to-indirect energy bandgap transition in armchair groups, while all the semiconductors of zigzag groups have a direct energy bandgap. We also study the effect of external transverse electric field on electronic properties. The applying electric field changes the energy bandgap leading to a semiconductor-to-metal transition at a certain electric field. In addition, the direct-to-indirect bandgap transition and vice versa occurs for some samples. Moreover, edge passivation has a significant effect on transport properties. The breakdown voltage of the devices changes from 0 to 1.94 eV, and we observe negative differential resistance (NDR) for some devices. The results indicate that passivated phosphorene nanoribbons are possible, and their properties can effectively be tuned by the arrangement, type of edge atoms, and external electric field, which make these structures a promising candidate for feasible nanodevices., QC 20220929

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1-delta OxN1-x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ~& nbsp;0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1-delta OxN1-x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1-delta OxN1-x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts. (C)& nbsp;2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.& nbsp

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al2OS as an efficient photocatalyst material for hydrogen-production H-2 through the first-principles calculations. Janus Al2OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al2OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al2OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al2OS, the absorption-coefficient of Janus Al2OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al2OS has been investigated. Our calculations demonstrate that the band edge position of Al2OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy Delta G(H*) of Al2OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga2XY (X, Y = S, Se, Te with X not equal Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/angstrom of an external electrical field. Our results indicate that Janus Al2OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting

Porphyrins constitute a class of attractive materials for harvesting sunlight and promote chemical reactions following their natural activity for the photosynthetic process in plants. In this work, we employ an in-silico design strategy to propose novel porphyrin-based materials as photocatalysts for hydrogen evolution reaction (HER). More specifically, a set of meso-substituted porphyrins with donor-acceptor architecture are evaluated within the density functional theory (DFT) framework, according to these screening criteria: i) broad absorption spectrum in the ultraviolet-visible (UV-Vis) and near infrared (NIR) range, ii) suitable redox potentials to drive the uphill reaction that lead to molecular hydrogen formation, iii) low exciton binding free energy (E-b), and iv) low hydrogen binding free energy (delta G(H)), a quantity that should present low HER overpotentials, ideally delta G(H) = 0. The outcomes indicate that the Se-containing compound, where the donor ligands are attached to the porphyrin core by the spacer, outstands as the most promising candidate that is presented in this work. It displays a broad absorption in the visible and NIR regions to up to 1000 nm, suitable catalytic power, low E-b (in special in high dielectric constant environment, such as water) and the lowest delta G(H) = +0.082 eV. This is comparable, in absolute values, to the value exhibited by platinum (delta G(H) =-0.10 eV), one of the most efficient catalysts for HER.

In the industrial large-scale chlor-alkali process, the electrocatalytic chlorine evolution reaction (CER) is a crucial half anodic reaction. However, the concomitant oxygen evolution reaction (OER) is unavoidable by using the noble metal-based dimensionally stable anodes (DSAs) as CER benchmark catalysts. Through purposely screening six TMN4 complexes embedded graphene with the demonstrated low performance of OER, our density functional theory (DFT) results predict that NiN4 complex embedded graphene (NiN4@G) can efficiently catalyse the CER. This single-atom catalyst (SAC) shows superior CER activity with the ultralow thermodynamic overpotential of 0.014 V via the Cl* intermediate instead of the formation of the ClO*. Moreover, its high theoretical overpotential of OER inherently promotes the selectivity of chlorine evolution. The analyses of the bonding mechanism between TM and Cl atoms reveal that their electrostatic attraction forces can be a good descriptor for the discovery of high-performance CER electrocatalysts. Our findings may broaden the scope of CER catalysts design beyond DSAs with the maximized metal atom utilization.

Gas sensors based on Carbon Nanotube (CNT) can be used to detect harmful environmental pollutants. Also, CNT has some unique electrical properties as gas sensor application. In this research, we have presented a new structure that is constructed from joining two similar Folded Armchair Graphene Nanoribbons (FAGNRs). Two FAGNRs are joined from their open sides, which make a CNT like device with noncircular cross section and we call it Attached FAGNR tube (AFAGNT). In addition to the physical properties we have investigated gas sensing performances of CNT and AFAGNT in presence of CO, O-2 and CO2 gases molecules. In this regards, our simu-lation results of AFAGNT show different significant sensitivities to CO gas molecule at various bias voltages, especially at 0.8V. On the other hand, CO2 gas molecule doesn't adsorb onto the AFAGNT which means it is not a CO2 gas sensor., QC 20220404

Industrial catalysts are often comprised of nanoparticles supported on high-surface-area oxides, in order to maximise the catalytically active surface area and thereby utilise the active material better. These nanoparticles expose steps and corners that, due to low coordination to neighboring atoms, are more reactive and, as a consequence, are often assumed to have higher catalytic activity. We have investigated the reaction between CO and preadsorbed O on a stepped Rh(553) surface, and show that CO oxidation indeed occurs faster than on the flat Rh(111) surface at the same temperature. However, we do find that this is not a result of reactions at the step sites but rather at the terrace sites close to the steps, due to in-plane relaxation enabled by the step. This insight can provide ways to optimize the shape of the nanoparticles to further improve the activity of certain reactions., QC 20211101

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1-delta OxN1-x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ~& nbsp;0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1-delta OxN1-x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1-delta OxN1-x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts. (C)& nbsp;2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.& nbsp

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al2OS as an efficient photocatalyst material for hydrogen-production H-2 through the first-principles calculations. Janus Al2OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al2OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al2OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al2OS, the absorption-coefficient of Janus Al2OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al2OS has been investigated. Our calculations demonstrate that the band edge position of Al2OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy Delta G(H*) of Al2OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga2XY (X, Y = S, Se, Te with X not equal Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/angstrom of an external electrical field. Our results indicate that Janus Al2OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting

Porphyrins constitute a class of attractive materials for harvesting sunlight and promote chemical reactions following their natural activity for the photosynthetic process in plants. In this work, we employ an in-silico design strategy to propose novel porphyrin-based materials as photocatalysts for hydrogen evolution reaction (HER). More specifically, a set of meso-substituted porphyrins with donor-acceptor architecture are evaluated within the density functional theory (DFT) framework, according to these screening criteria: i) broad absorption spectrum in the ultraviolet-visible (UV-Vis) and near infrared (NIR) range, ii) suitable redox potentials to drive the uphill reaction that lead to molecular hydrogen formation, iii) low exciton binding free energy (E-b), and iv) low hydrogen binding free energy (delta G(H)), a quantity that should present low HER overpotentials, ideally delta G(H) = 0. The outcomes indicate that the Se-containing compound, where the donor ligands are attached to the porphyrin core by the spacer, outstands as the most promising candidate that is presented in this work. It displays a broad absorption in the visible and NIR regions to up to 1000 nm, suitable catalytic power, low E-b (in special in high dielectric constant environment, such as water) and the lowest delta G(H) = +0.082 eV. This is comparable, in absolute values, to the value exhibited by platinum (delta G(H) =-0.10 eV), one of the most efficient catalysts for HER.

This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

In this present work, the investigation was carried out using density functional theory (DFT) for the dissociation of noxious gas molecules such as carbon and nitrogen-based molecules (CO, CO2, N-2, NH3, NO, and NO2) on a pentagonal two-dimensional beryllium diphosphide (BeP2). The pentagonal BeP2 monolayer has a similar band structure as graphene. Here, some carbon and nitrogen-based noxious gases such as CO, CO2, N-2, NH3, NO, and NO2 with Van der Waals (vdW) interaction behave like physisorbed, while strong covalent (Be-O) interactions of O-2 on BeP2 formed chemisorption. Due to the chemisorption of O-2 gas molecules, the bandgap at Dirac point at P-site on BeP2 opens. While CO, CO2, N-2, NO, and NO2 are dissociated at the C-site, only CO, N-2, and NO are dissociated at the P-site. Beryllium diphosphide's band-gap shifts resulting from interactions with CO, N-2, and O-2 molecules are just 6%, 12.1%, and 22.2%, respectively, meaning that the BeP2 material has a moderate and high sensitivity towards CO, N-2, and O-2 molecules. BeP2 appears to be a potential catalyst for the dissociation of CO, CO2, N-2, NO, NO2, and O-2 gas molecules, which is even more interesting.

Recent development in two-dimensional materials is due to their exceptional performances in the field of electronics and optical devices in the nano regime. First principles investigation based on density functional theory is used to predict the existence of Li2O in two-dimensional hexagonal monolayer flatlands. Li2O is found to be in H- and T-phase honeycomb structures in monolayer regime. The structural stability was confirmed by phonon calculation which suggests their potential experimental realization. The mechanical properties of both Hand T-phases of Li2O is calculated, the in-plane stiffness of both phases are 10.56% and 15.77% of graphene whereas the Poisson ratio for both phases are more than 1.5 times that of graphene. The electronic band structure calculation reveals that H phase of Li2O is metallic in nature, while the T phase exhibits direct band gap of 2.87 eV. Further, the optical properties for both H and T phases of Li2O suggests their potential applications in optical devices. Present results enlighten that this new two-dimensional Li2O can be utilized to develop stable and efficient optoelectronic materials.

In this theoretical study, based on the density functional theory, we investigate the electronic, optical and thermoelectric properties of SiGeC4 nanosheet, within the framework of mBJ-GGA approximation (modified Becke-Johnson generalized gradient approximation). The calculated results indicate that the two-dimensional SiGeC4 compound is energetically, dynamically, thermally and mechanically stable in the pentagonal structure and shows semiconductor character with indirect and moderate bandgap. Also, it is found that this two-dimensional system presents high absorption and low reflectivity as well as high photoconductivity in the visible range. Furthermore, it is shown that the studied compound exhibits good thermoelectric performance with high electrical conductivity and Seebeck coefficient. These results render the twodimensional pentagonal SiGeC4 nanosheet as strong absorber layer candidate in the next generation of photovoltaic devices.

Titanium aluminides are technologically important intermetallic alloys with also many curious properties interesting from a basic research point of view. When alloyed with Mo, several (meta)stable phases have been reported; their properties are, however, largely unknown due to the alloy processing (e.g. fast cooling) and/or non-existence as a single-phase material. Here we employ first principles calculations to study compositional trends in structural and mechanical properties. We could show that Mo increases the density of all studied phases, leads to their chemical destabilization with the exception of the ordered bcc /3o phase, increases their ductility, and enhances the elastic anisotropy. Discrepancies between two employed ab initio methods (special quasi-random structures vs. coherent potential approximation) in the case of the /3o and B19 phases are rationalized with significant local distortions which may eventually facilitate a spontaneous phase transformation. Predictions of ordering temperatures solely based on the configurational entropy do not yield values in the experimentally expected ranges., QC 20211201

This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

Detection and sensing of toxic gases are vital in many areas such as in environmental and safety monitoring, industrial applications and etc. Fundamental requirements for modern gas sensors typically are small size, low power consumption, high sensitivity and good selectivity towards various gases. Recently, graphene-based gas sensors have attracted significant attention due to their potential applications. Based on published works, the energy band gap of monolayer graphene nanoribbon (GNR) varies by changing its ribbon width. However, in the case of bilayer GNR, the energy band gap varies via three ways: the ribbon width, the layers separation and the symmetry between the layers. Therefore, it is interesting to investigate the characteristics of bilayer armchair graphene nanoribbon (B-AGNR) as gas nanosensor in presence of CO, O-2 and CO2 gas molecules. In this study, we report a theoretical investigation and numerical simulation of the electronic properties of monolayer and bilayer AGNR (with 10 atoms in width) and study their sensitivities in presence of CO, O-2 and CO2 gas molecules. Using Quantum espresso-5.3.0 package, the structure optimizations are done based on density functional theory (DFT). Moreover, we have evaluated the current-voltage (I-V) characteristics of the aforementioned structures using the open source package TRAN SIESTA which is based on non-equilibrium Green's function (NEGF) method. The obtained results show that the adsorption of CO, O-2 and CO2 gas molecules onto AGNR can be modified significantly in bilayer AGNR with respect to the monolayer. These gas molecules show weak interaction with the AGNR atomic structure due to large interaction distances. Thus, it is deduced that the graphene nanoribbon (AGNR) shows weak gas sensing in presence of CO, O-2 and CO2 molecules. Meanwhile, bilayer AGNR shows different electronic properties compared to monolayer AGNR which makes it highly sensitive and selective to the presence of O-2 and CO gases., QC 20210420

For an envisioned hydrogen (H2) economy, the design of new multifunctional two-dimensional (2D) materials have been a subject of intense research for the last several decades. Here, we report the thriving H2 storage capacity of 2D nitrogenated holey graphene (C2N), functionalized with Tin (n = 1–5) clusters. By using spin polarized density functional theory (DFT) calculations implemented with the van der Waals corrections, the most favourable adsorption site for the Tin clusters on C2N has been revealed. With the monomer Ti, the functionalization was evenly covered on C2N having 5% doping concentration (C2N–Ti). For C2N–Ti sheet, Ti binds to C2N with a strong binding energy of ~6 eV per Ti which is robust enough to hinder any Ti–Ti clustering. Bader charge analysis reveals that the Tin clusters donate significant charges to C2N sheet and become cationic to polarize the H2 molecules, thus act as efficient anchoring agents to adhere multiple H2 molecules. Each Ti in C2N–Ti could adsorb a maximum of 10H2 molecules, with the adsorption energies in the range of −0.2 to −0.4 eV per H2 molecule, resulting into a high H2 storage capacity of 6.8 wt%, which is promising for practical H2 storage applications at room temperature. Furthermore, Tim (m = 2, 3, 4, 5) clusters have been selectively decorated over C2N. However, with Tim functionalization H2 storage capacities fall short of the desirable range due to large molecular weights of the systems. In addition, the H2 desorption mechanism at different conditions of pressure and temperature were also studied by means of thermodynamic analysis that further reinforce the potential of C2N–Ti as an efficient H2 storage material., QC 20211110

The metallic ternary compound phase of S-P-H material is predicted to be the ground-state structure by first principles cluster expansion. We find that the S0.75P0.25H3, S0.5P0.5H3, and S0.25P0.75H3 structures are thermodynamically stable. The characteristic of phonon dispersions shows that the S0.75P0.25H3 and S0.5P0.5H3 structures are dynamically stable at 200 GPa. The solution of the Fermi surface supports the values of superconducting transition temperature (Tc). In addition, the electron localization function and the projected crystal orbital Hamilton populations reveal that the nature of chemical bonding shows the degree of covalent bonding of the S0.75P0.25H3 and S0.5P0.5H3 structures, supporting the Tc value. Our results show that the S0.5P0.5H3 structure is the highest Tc among the S-P-H system. The Tc of the S0.5P0.5H3 structure is estimated to be 89 K at 200 GPa., QC 20210323

In recent years, several two-dimensional (2D) materials with semiconducting electronic properties have been introduced. The ZrSe2 (Zirconium diselenide) is one of the best materials to replace the silicon in nanoelectronics due to its proper bandgap. In this research, we study the electronic properties of the armchair and zigzag ZrSe2 nanoribbons (AZSNRs and ZZSNRs). Moreover, we have investigated the effect of edge passivation of two 3AZSNR and 3ZZSNR (the ribbon width is 3) structures with hydrogen (H) and oxygen (O) atoms and also both of them (H/O) concurrently. By calculating the cohesive energy of all structures, we deduce that all zigzag and armchair structures with different edge passivations are stable and energy favorable. Also the edge passivation with H-O atoms can change the electronic properties of 3ZZSNR structure significantly, and the structure behavior changes from semiconductor to metallic. In the case of the armchair structures, the edge passivated structure with O atoms (3AZSNR-O) is the most stable and feasible to fabricate in nanoscale experiments. These results show that the ZrSe2 nanoribbons with different edge passivations have potential applications in nanoelectronics., QC 20210318

Green phosphorus and its monolayer variant, green phosphorene (GreenP), are the recent members of two-dimensional (2D) phosphorus polymorphs. The new polymorph possesses the high stability, tunable direct bandgap, exceptional electronic transport, and directionally anisotropic properties. All these unique features could reinforce it the new contender in a variety of electronic, optical, and sensing devices. Herein, we present gas-sensing characteristics of pristine and defected GreenP towards major environmental gases (i. e., NH3, NO, NO2, CO, CO2, and H2O) using combination of the density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green's function approach (NEGF). The calculated adsorption energies, density of states (DOS), charge transfer, and Crystal Orbital Hamiltonian Population (COHP) reveal that NO, NO2, CO, CO2 are adsorbed on GreenP, stronger than both NH3 and H2O, which are weakly physisorbed via van der Waals interactions. Furthermore, substitutional doping by sulfur can selectively intensify the adsorption towards crucial NO2 gas because of the enhanced charge transfer between p orbitals of the dopant and the analyte. The statistical estimation of macroscopic measurable adsorption densities manifests that the significant amount of NO2 molecules can be practically adsorbed at ambient temperature even at the ultra-low concentration of part per billion (ppb). In addition, the current-voltage (I–V) characteristics of S-doped GreenP exhibit a variation upon NO2 exposure, indicating the superior sensitivity in sensing devices. Our work sheds light on the promising application of the novel GreenP as promising chemical gas sensors. © 2020 Elsevier B.V., QC 20201203.QC 20210408

We design high entropy alloys (HEAs) with different induction elements (Si/Al/Sn). In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization (Ms) is caused only by the change of electron spin state, each set of HEAs contains a different amount of Mn. Synergistic effects among induction elements that induce the magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism are found. Ms of added Mn reduces when a particular induction element (Si0.4/Al0.4/Sn0.4) exists, while a larger increment of Ms appears when two induction elements coexist, Si0.4Al0.4 (25.79 emu/g) and Sn0.4Al0.4 (15.43 emu/g). This is reflected in the microcosmic magnetic structure for the emergence of closed domains due to large demagnetization energy, which is confirmed by the Lorentz transmission electron microscope (LTEM) data. The calculated magnetic moments and the exchange integral constants from density functional theory based on the Exact Muffin-Tin Orbits formalism reveal that the magnetic state and the strength of ferromagnetic and anti-ferromagnetic coupling determine the variation of Ms in different chemical environments. The difference in energy levels of coexisting multiple induction elements also leads to a larger increment of Ms, Si0.4Al0.4Sn0.4 (29.78 emu/g), and Si0.4Al0.4Ge0.4Sn0.4 (31.00 emu/g)., QC 20201112

Ketene, a versatile reagent in production of fine and specialty chemicals, is produced from acetic acid. We investigate the synthesis of ketene from acetic acid over the (3,0;1,1) surface of Cu2O(100) through analysis of the adsorption and desorption characteristics of formic and acetic acids. The results allow us to establish a reaction mechanism for ketene formation. Observations from x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, and temperature programmed desorption (TPD), supported by a comparison with formic acid results, suggest that acetic acid reacts with Cu2O through deprotonation to form acetate species coordinated to copper sites and hydroxylation of nearby surface oxygen sites. For formic acid the decomposition of adsorbed formate species results in desorption of CO2 and CO while, for acetic acid, high yields of ketene are observed at temperature >500 K. Modeling by density functional theory (DFT) confirms the strong interaction of acetic acid with the (3,0;1,1) surface and the spontaneous dissociation into adsorbed acetate and hydrogen atom species, the latter forming an OH-group. In an identified reaction intermediate ketene binds via all C and O atoms to Cu surface sites, in agreement with interpretations from XPS. In the vicinity of the adsorbate the surface experiences a local reorganization into a c(2 x 2) reconstruction. The total computed energy barrier for ketene formation is 1.81 eV in good agreement with the 1.74 eV obtained from TPD analysis. Our experimental observations and mechanistic DFT studies suggests that Cu2O can operate as an efficient catalyst for the green generation of ketene from acetic acid., QC 20211021

This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

Point defects in body-centred cubic Fe, Cr and concentrated random magnetic Fe-Cr are investigated using density functional theory and theory of elasticity. The volume of a substitutional Cr atom in ferromagnetic bcc Fe is approximately 18% larger than the volume of a host Fe atom, whereas the volume of a substitutional Fe atom in antiferromagnetic bcc Cr is 5% smaller than the volume of a host Cr atom. In an alloy, elastic dipole P and relaxation volume omega tensors of vacancies and self-interstitial atom (SIA) defects exhibit large fluctuations, with vacancies having negative and SIA large positive relaxation volumes. Dipole tensors of vacancies are nearly isotropic across the entire alloy composition range, with diagonal elements Pii decreasing as a function of Cr content. Fe-Fe and Fe-Cr SIA dumbbells are more anisotropic than Cr-Cr dumbbells. We find that fluctuations of elastic dipole tensors of SIA defects are primarily associated with the variable crystallographic orientations of the dumbbells. Statistical properties of tensors P and omega are analysed using their principal invariants, suggesting that point defects differ significantly in alloys containing below and above 10% at. Cr. The von Mises stresses caused by dumbbells are notably larger than those caused by vacancies. The relaxation volume of a vacancy depends sensitively on whether it occupies a Fe or a Cr lattice site. A correlation between elastic relaxation volumes and magnetic moments of defects found in this study suggests that magnetism is a significant factor influencing elastic fields of defects in Fe-Cr alloys., QC 20210720

This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

The multicomponent Ti alloys, specifically the fl-phase, have experienced a strong growth over the last decades, due to their outstanding properties of ultra-high strength and low Young's modulus. These properties play a significant role in many aerospace and biomedical applications. Selection and optimization of multicomponent alloys is challenging due to the vast chemical and compositional space. Here we investigate the use of machine learning techniques informed by density functional calculations to guide the selection of Nband Zr-based Ti binary alloys. From the cubic structures obtained from high throughput calculations and literature, we identify several structures with Young's moduli below 40 GPa. The multivariant decision tree methods provide efficient surrogate models to identify structure variables have high influences on the energetic stability and Young's modulus. We implement a workflow of incorporating DFT provided results and machine learning method to explore the chemical and composition space of other binary and multicomponent alloys, to eventually accelerate the material design via taking advantages of identified key variables.

An analog of graphene, graphitic carbon nitride (g-C3N4), is a promising metal-free conjugated polymer, owing to its excellent performance in biosensing and photocatalysis. We have demonstrated the adsorption of twenty-five amino acids (AA) employing DFT-D3 correction method of Grimme's dispersion and the non-equilibrium Green's function (NEGF) for describing the coherent transport in molecular devices coupled with adsorption energies, substrate-adsorbate distances, the density of states, charge transfer mechanism, molecular dynamics, work function, and bonding patterns. We have also depicted the current-voltage (I-V) characteristics where the curves of current vs. bias voltage (I-V-b) display a distinct response for each AA. Furthermore, we have illustrated the anti-bacterial mechanism of g-C3N4 utilizing bioinformatics study and compared it with DFT studies. We found evidence of a difference in transport, electronic as well as molecular mechanisms reinforcing the possibility of g-C3N4 applications based on sensors for AA sequencing of proteins, water-disinfection technique, and microbial control., QC 20201113

Amongst promising available technologies enabling the transition to renewable energy sources, electrochemical oxidation of alcohols, in a direct fuel cell or in an electrolysis reaction (H-2 production), can be an economically and sustainable alternative to currently used technologies. In this work, we highlight the advantages of a Pd-Ni bimetallic electrocatalyst for methanol electrooxidation - a convenient choice due to the low cost of Ni combined with the observed acceptable catalytic performance of Pd. We report a synergistic effort between experiments and theoretical calculations based on density functional theory to provide an in-depth understanding - at the atomistic level - of the origin of the enhanced electrochemical activity of methanol electrooxidation using the bimetallic catalysts Pd3Ni and PdNi over pure Pd. Cyclic voltammograms and High-Performance Liquid Chromatography (HPLC) demonstrate higher activity towards methanol electrooxidation with increased Ni concentration and, furthermore, higher selectivity for CO2. These effects are understood by: 1) changes in the methanol oxidation reaction mechanism. 2) Mitigation or suppression of CO poisoning on the Pd-Ni alloys as compared to the pure Pd catalyst. 3) A stronger tendency towards highly oxidized intermediates for the alloys. These findings elucidate the effects of a bimetallic electrocatalyst for alcohol electrooxidation as well as unambiguously suggest PdNi as a more cost-effective alternative electrocatalyst., QC 20201126

The stability of constituent phases in multi-component system always plays a prominent role in tailoring their mechanical performance at elevated temperatures. In this work, we highlight a chemical ordering feature in the AlTiVCr1-xNbx (0 <= x <= 1) alloys with body-centered cubic crystal structure. The quantum-mechanical first-principle investigations of these alloys on the elemental distribution identify a family of B2 type of partially ordered configurations. We map out the elastic parameters in detail as a function of composition and temperature for disordered and partially ordered phases. A great sensitivity to the order-disorder transformation is revealed, especially for the Cr-rich system. Our results demonstrate that a proper control of the ordering level in these alloys can facilitate the optimal tuning of their mechanical performance while keeping the density almost unchanged. The study presented here further predicts that these alloys possess high specific stiffness, low thermal expansion, and large elastic softening resistance. It is demonstrated that the considered alloys have thermal and mechanical properties that compete with superalloys and other high temperature structural materials., QC 20201113