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The emergence of oxygenic photosynthesis was a major event in Earth's evolutionary history and was facilitated by chlorophylls (a major category of photopigments). The accurate modelling of photopigments is important to understand the characteristics of putative extraterrestrial life and its spectral signatures (detectable by future telescopes). In this paper, we perform a detailed assessment of various time-dependent density-functional theory (TD-DFT) methods for predicting the absorption spectra of chlorophyll a, with particular emphasis on modern low-cost approximations. We also investigate a potential extraterrestrial photopigment called phot0 and demonstrate that the electronegativity of the metal ion may exert a direct influence on the locations of the absorption peaks, with higher electronegativity inducing blue-shifting and vice-versa. Based on these calculations, we established that global-hybrid approximations with a moderate percentage of exact exchange – such as M06 and PW6B95 – are the most appropriate compromise between cost and accuracy for the computational characterisation of photopigments of astrobiological interest. We conclude with a brief assessment of the implications and avenues for future research. [ABSTRACT FROM AUTHOR]

This paper adopted the 2D periodic boundary-condition (PBC) density functional theory (DFT) to examine the adsorption of CH3Br, CH3Cl, and CH3F halomethanes into not only bare boron phosphide (BP) nanosheets but also gallium- and aluminium-doped ones. Geometric optimisation was applied to all the structures at the B3LYP/6-311+G (d) level of theory. Moreover, the CAM-B3LYP/6-311+G(d), ωB97X-D3, and M06-2X levels of theory were implemented to calculate the single point energy. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were carried out, evaluating the donor-acceptor interactions, partial natural charge, and Wiberg bond index (WBI). The adsorption energy values demonstrated that the gallium-doped BP had the highest adsorptive capability, while the lowest adsorption occurred in the bare BP. However, the adsorption of CH3Cl, with much smaller adsorption energy, was maximised in the aluminium-doped BP and minimised in the bare BP. Furthermore, CH3Br and CH3Cl showed the highest and lowest tendencies to be adsorbed onto the nanosheet surfaces, respectively. Gallium- and aluminium-doped BP structures appear to be efficient and effective in the development of new solid-state sensors of halomethanes. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes (OLEDs) have been widely used in various fields such as sensors. In this article, we designed six novel heterocyclic Ir(III) complexes: (CFM)2Ir(acac) (named 1 in this paper), (TTIQ)2Ir(acac) (named 2), (CFM)2Ir(tmd) (named 3), (TTIQ)2Ir(tmd) (named 4), (CFM)2Ir(pic) (named 5) and (TTIQ)2Ir(pic) (named 6). The six iridium (III) complexes were calculated using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). We studied the bands of the lowest-lying absorptions and lowest energy emissions of complexes 1–6. In addition, we also explored their spectral properties, frontier Molecular Orbital theory(FMO) and spin-orbital coupling value(SOC). Where acac is represented as pentane-2, 4-dione; tmd as 2,2,6,6-tetramethylheptane-3,5-dione; pic as pyridine-2-carboxylate; TTIQ as 1- { thieno[3,2-b]thiophen-2-yl } isoquinoline; CFM as 2-(4-fluorobrobenyl)-4-methylpyridine. A series of heteroleptic cyclometalated Ir (III) complexes, which are used for OLED application, were investigated by DFT and TD-DFT method. The frontier molecular orbital character and charge transfer character shown that they have the advantages of low efficiency roll-off properties, which is a 'stumbling block' in the process of OLED solid-lighting's development. Namely, means the materials will play an important role in the journey development of OLED. [ABSTRACT FROM AUTHOR]

The reduction of CO2 into clean energy through electro catalytic technology provides a promising solution to alleviate energy shortages. In this paper, the graphitised material-supported metal dimer used for electro catalytic reduction of CO2 was proposed, and the reduction reaction mechanism was explored by density functional theory. The results indicate that the hydrogenation reduction of CO2 tends to occur preferentially, and it was found that improving the stability of catalyst structure can reduce the free energy of reaction and improve the adsorption effect of reactants, which significantly increase the conversion efficiency of CO2. The activation of CO2 on the catalyst surface is closely related to the binding of O atoms on the metal sites, the main reduction products and their reaction pathways were clarified. The reduction over potentials of CuCo-C, CuRh-C, CuZn-C and ZnCu-C were 0.915, 0.820, 0.774, and 0.354 V, respectively, thus ZnCu-C had a lower reduction over potential and higher catalytic efficiency. [ABSTRACT FROM AUTHOR]

Diversely functionalised pyrazolone analogues have been reported to display a wide range of biological activities. In this paper, we report the synthesis of a series of novel analogues based on piperidine fused pyrazolone core and explore its potential as novel antibacterial agents. The synthesised compounds were analysed using spectroscopic techniques such as 1H NMR, LC-MS, and FT-IR. The major highlight involves the cyclisation reaction of tert-butyl-4-methyl 3-oxopiperidine-1,4-dicarboxylate with the hydrazine component to access the privileged piperdine fused pyrazolone scaffold. This scaffold was further treated with HCl to remove the amine protecting group and subsequently reacted with acid chlorides to deliver the final products in excellent yields. Density functional theory (DFT) calculations were performed to determine the various molecular properties of the synthesised compounds. Based on the reactive sites explored by the molecular electrostatic potential maps, the compounds were screened against two gram positive bacterial strains namely S. aureus, and M. luteus, and a gram negative bacterial strain namely E.coli. Highlights A Series of novel pyrazole derivatives were synthesised using bicyclisation strategy. Computational methods were used to determine various quantum chemical properties. All molecules were screened against S. aureus, M. luteus, and E. coli bacterial strains. [ABSTRACT FROM AUTHOR]

Orientation arrangement of hydration shells for hydrated cation plays an important role in solid–liquid interfaces. However, there is still poor understanding about the structure of the hydration shells formed at the solid–liquid interface. In this paper, we study the structures and interaction of typical hydrated alkali metal cation (Li+, Na+ and K+) on the flat polar material surface of the hexagonal boron nitride (h-BN) sheet by increasing the number of water molecules from n = 1 to n = 9 through the artificial bee colony (ABC) algorithm and density functional theory calculations. The hydration shell around alkali metal cation could be divided into two groups, one is Li+-(H2O)n and Na+-(H2O)n and the other is K+-(H2O)n. The orientation of hydration shell for K+-(H2O)n complexes exhibits stronger anisotropy behaviour than both Li+-(H2O)n and Na+-(H2O)n complexes on the h-BN sheet. It is found that the stronger orientation anisotropy of K+-(H2O)n originates from the weak cation-hydration energy and its weak influence upon the π-K+ interaction. Our findings provide valuable insights into the microscopic details of the structures and adsorption of hydrated cation on the h-BN sheet. [ABSTRACT FROM AUTHOR]

Iron-based catalysts can be used as de-NOx catalysts due to their good adsorption performance to gas molecules. However, the adsorption behaviours of NH3, NO, and O2 molecules on ferrous oxide surface are unclear. In this paper, the adsorption properties of NH3, NO, and O2 molecules over FeO (100) surface and oxygen-defected FeO (100) surface were studied by a density functional theory calculation. The Fe-top of the FeO (100) surface is the most active site. NH3 and NO can be adsorbed on the Fe-top sites by N terminal. The adsorption of O2 on the Hollow site of the FeO (100) surface has a larger adsorption energy. When oxygen-defected presents on the FeO (100) surface, the adsorption performances of NH3 and NO on the Fe-top sites are slightly decreased. NO and O2 can be adsorbed on the O-defected site, in which the adsorption energy of O2 is larger. For the adsorption of double molecules, O2 + NH3 or O2 + NO adsorbed on the FeO (100) surface have synergistic effects, respectively, which enhance the adsorption performance. Moreover, the co-adsorption behaviours of O2 + NH3 and O2 + NO on the O-defected FeO (100) surface also occur. [ABSTRACT FROM AUTHOR]

Great research interest in the novel P-based nanosensors has been spurred by the arrival of black phosphorus monolayer devices in recent years. The paper investigates the detection capabilities of defective phosphorene (DP) toward the sensing of cyanogen fluoride and chloride molecules using periodic density functional theory. As found from the optimizations, the analyte stabilisation in the lowest-energy configuration is non-linear with the molecule interacting through the nitrogen head. The fluoride molecule released 2.5 times higher energy (–15.63 kcal/mol at HSE06/TZVP) than the chloride counterpart upon the adsorption on the surface. Significant changes were seen in both spin gaps of DP with sensing, particularly in the case of CNCl. The sensitivity and air selectivity for the system under consideration amounted to 9.9 and 50.4, respectively. Overall, the findings reported herein confirmed that the defective phosphorene (DP) sensor can be used for cyanogen halides detection, with the recovery time of up to 290.0 ms at 298 K. [ABSTRACT FROM AUTHOR]

Technology has developed as a result of computerisation, and a wide range of other fields, such as physics and chemistry, have been involved in the application of machine learning. nodes and edges together form a crystal so that it is easy to represent as a graph. Some typical models such as MEGNET show good generalisation in material property prediction by using a graph neural network instead of the traditional density functional theory(DFT). The author proposes a fusion self-attention graph neural network (FSGN) model that incorporates a graph neural network with fusion and attentional mechanisms to predict material properties. The convolutional self-attention module is mainly used to extract the importance of autocorrelation and cross-correlation in node, edge and global information. Multi-head attention feature fusion is used after shallow additive fusion to get more discriminative features. Compared with other Machine Learning models like MEGNET and CGCNN, it can be demonstrated that the prediction accuracy(ACCU) of our model has been improved to some extent. [ABSTRACT FROM AUTHOR]

In this paper, the growth pattern, magnetic and electronic structure of VLin (n = 2–13) clusters are studied using density functional theory in generalised gradient approximation. The growth pattern showed that the VLin (n = 2–13) clusters favoured the three-dimensional configuration and appeared cage-like structures with increasing size. The average binding energy, second-order energy difference and dissociation energy are discussed, and the VLi12 cluster is magnetic superatom. The spin magnetic moment of VLi12 cluster is 1 μB and the molecular orbital arrangement is 1S21P61Dα51Dβ4. The chemical bonding patterns of the VLi12 cluster was obtained by using molecular orbital analysis and the adaptive natural density partitioning method. [ABSTRACT FROM AUTHOR]

Molecules containing sulfur play an important role in atmospheric chemistry, but their reactivity in such environment is far from being well characterised. Therefore, important transient species might still have to be disclosed. In this regard, this paper aims at contributing to this field by means of the computational spectroscopic characterisation of potentially relevant atmospheric species, such as the CH 2 O 2 S isomers. Based on our computational investigation, the most stable species are the carbonothionic O,S- and O,O-acids. In addition to them, the sulfene molecule has also been considered. For all these species, the equilibrium structure and the corresponding rotational constants have been accurately evaluated using a coupled-cluster-based composite approach. All the other parameters required for the simulation of the rotational and ro-vibrational spectra have been obtained by exploiting density functional theory. [ABSTRACT FROM AUTHOR]

The good performance of a photovoltaic device requires fitting a series of parameters related to electronic structure of materials. Since it is well-known that fullerenol is an excellent electron acceptor with excellent electron conductivity, in this paper we analyse the electronic levels, energy gaps, absorption spectra and electron mobility of hydroxylated La@C 82 (La@C 82 (OH) n , n = 0−32) endohedral metallofullerene. Furthermore, calculations was performed on one unit of three donor polymers with low energy of the lowest unoccupied molecular orbital and on the well-known acceptor fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) in order to compare the electronic structure and possible donor–acceptor combinations. Interestingly, high coatings have larger energy gap between the highest occupied molecular orbital of donor and the lowest unoccupied molecular orbital of acceptor, which is essential for increasing the open circuit voltage, which relates directly to power conversion efficiency. On the other hand, low coatings have better electron mobility, which is essential in electron transport layers in perovskite-based solar cells. Finally, the absorption spectra of fullerenols were also calculated and compared with the widely used in organic solar cells PC 61 BM, obtaining a broader absorption spectrum in hydroxylated endohedral metallofullerenes helping in the performance of fullerenols for harvesting the solar spectrum. [ABSTRACT FROM AUTHOR]

We have in a series of recent papers investigated electronic excited states with a hybrid between a complete active space self-consistent field (CASSCF) wave function and density functional theory (DFT). This method has been dubbed the CAS short-range DFT method (CAS–srDFT). The previous papers have primarily focused on the excitation energies, and not on the oscillator strengths, although they comprise an important part of the absorption spectrum. In this study, we have carried out a quantitative analysis of oscillator strengths obtained with CAS–srDFT. As target molecules, we have considered the large collection of organic molecules whose excited states were investigated with a range of electronic structure methods by Thielet al. As a by-product of our calculations of oscillator strengths, we also obtain electronic excitation energies, which enable us to compare the performance of CAS–srPBE for excitation energies, using a larger set of chromophores compared to previous studies. [ABSTRACT FROM AUTHOR]

In this paper, Lafuente and Cuesta's cluster density functional theory (CDFT) and lattice mean field approximation (LMFA) are formulated and compared within the framework of lattice density functional theory (LDFT). As a comparison, an LDFT based on our previous work on nonrandom correction to LMFA is also developed, where local density approximation is adopted on the correction. The numerical results of density distributions of an Ising fluid confined in a slit pore obtained from Monte Carlo simulation are used to check these functional approximations. Due to rational treatment on the coupling between site-excluding entropic effect and contact-attracting enthalpic effect by CDFT with Bethe-Peierls approximation (named as BPA-CDFT for short), the improvement of BPA-CDFT beyond LMFA is checked as expected. And it is interesting that our LDFT has a comparative accuracy with BPA-CDFT. Apparent differences between the profiles such as solvation force, excess adsorption quantity and interfacial tension from LMFA and non-LMFAs are found in our calculations. We also discuss some possible theoretical extensions of BPA-CDFT. [ABSTRACT FROM AUTHOR]

In this paper, the non-local density functional theory is used in combination with SAFT-VR, to investigate the pore pressure behaviour of water confined in various nanopores. Due to the efficiency and low computational cost of the method, many configurations and thermodynamic conditions are explored. In particular, capillary condensation and evaporation of water, their impact on the pore pressure, and the effect of surface activation are evaluated. Successive first-order phase transitions of ultra-confined water monolayer are also highlighted. [ABSTRACT FROM AUTHOR]

Density functional theory and the non-equilibrium Green's function are combined to investigate the co-modulation effect of endohedral Au atom and anchor S atoms on C 20 . In this paper, anchor atoms Au and S are used, respectively, to connect the endohedral fullerene C 20 with Au nanowires, respectively. Both density of states and transmission coefficient as functions of energy and voltage are investigated to evaluate the spin interaction between molecular orbital and itinerant electrons and explain the influence on current–voltage dependence of C 20 . The results show that different combination of endohedral and anchor atoms can promote or inhibit the transmission probability of itinerant electrons. Co-modulation cannot only present more abundant transmission properties but also form spin asymmetric transmission peaks that may perform new nano circuit functions. [ABSTRACT FROM AUTHOR]

The aim of this paper is a better comprehension of the encapsulation and interaction an anticancer drug Altretamine into BN nano ring [BNNR(9,9-5)] and AlN nano ring [AlNNR(9,9-5)]. The electronic and adsorption properties of the molecule Altretamine over the BNNR and AlNNR were theoretically studied in the solvent phase at the B3LYP/6-31G* level of theory for the first time. With the non-bonded interaction of Altretamine, the electronic properties of the BN and AlN nano-cages can be significantly changed. The electronic spectra of the Altretamine drug, complex BNNR/Altretamine and AlNNR/Altretamine in solvent water were calculated by Time Dependent Density Functional Theory (TD-DFT) for the investigation of adsorption effect. According to the natural bond orbital (NBO) results, the molecule Altretamine, BNNR and AlNNR play as both electron donor and acceptor at the complexes BNNR/Altretamine and AlNNR/Altretamine. On the other hand, the charge transfer is occurred between the bonding, antibonding or nonbonding orbitals in the molecule drug, BNNR and AlNNR. As a consequence, BNNR(9,9-5) and AlNNR(9,9-5) can be considered as a drug delivery system for the transportation of Altretamine as anticancer drug within the biological systems. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT)-based calculations were performed for 36, 72 and 108 water molecules forming twisted ribbon-like nano-ring structures of diameter 1.54, 3.10 and 4.56 nm, respectively. We explore the electric field evolution of the structure, energetics and stability of the water nano-ring structures that are essentially symmetric and non-polar, or less-symmetric and polar, hydrogen-bonded clusters. The results suggest that for fields applied perpendicular to the ring, larger rings are more susceptible to the field influence, while fields applied parallel to the ring quickly transform the ring structures into arbitrary ones, regardless of the ring size. Infrared and Raman spectral analysis of local modes demonstrate the typical vibrational response of water molecules to various H-bonding environments and applied fields, providing a spectroscopic signature that can be used to identify the manifestation of such H-bonded ring networks. Our study underscores the implications of the nano-sized ring water clusters, which have the potential to be exploited in a variety of device applications. [ABSTRACT FROM AUTHOR]

Radiative efficiency (RE) is a key climate metric used in the evaluation of a greenhouse gases global warming potential. However, experimental methods are commonly limited to measurements in the spectral region greater than ∼500 cm−1. In this study, density functional theory with the wB97X-D/def2TZVPPD level of theory was employed to calculate the infrared absorption spectra and the contribution of the 0–500 cm−1 spectral region to the total RE for the nearly 800 greenhouse gases, 20 different classes of primarily halogenated compounds, included in the World Meteorological Organization (WMO) Scientific Assessment of Ozone Depletion Annex [1]. In general, the results indicate that the contribution of the low-frequency regime to the total overall RE is not significant, < 2%, with a few exceptions, e.g. several compounds in the hydrocarbon class. [ABSTRACT FROM AUTHOR]

Oxidative decomposition of solid lithium peroxide is an important part of the charging process in a Li-O2 battery. In this paper, we investigate oxidative decomposition mechanisms of lithium peroxide clusters as molecular models for solid lithium peroxide using density functional methods to understand charging processes in advanced energy storage systems. Most calculations are done using a (Li2O2)4 cluster with similar results obtained from a larger (Li2O2)16 cluster. Reaction pathways of the clusters involving different sequences of oxidation, oxygen evolution, lithium cation removal, and spin excitation are investigated. The computations suggest that certain oxidative decomposition routes may not have dependence on the oxygen evolution or Li-ion removal kinetics due to the exothermicity of oxygen removal and Li+ removal (by solvent) upon oxidation. The computed charge potentials evaluated using a tetramer model indicates that it is possible to have low overcharge potential provided there exists a good electronic conductivity to facilitate the oxidative decomposition. Finally, oxidation potentials of a series of LixOy clusters are investigated to assess their dependence on stoichiometry and how the local site from which the electrons are being removed affects the charge potentials. [ABSTRACT FROM AUTHOR]

Inverted perovskite solar cells (PSCs) have attracted much attention due to their low-temperature and solution-based process. Electron transport layers are important components in inverted PSCs. Non-fullerene n-type organic small molecules seem to be more attractive as electron transport layers, because their structures are easy to be synthesised and modified. In this paper, density functional theory and semi-classical Marcus electron transfer theory were used to explore the electron transport properties in three azaacene derivatives, including one experimentally reported molecule, 1,4,9,16-tetrakis((triisopropylsilyl)ethynyl)quinoxalino[2‴,3‴:4″,5″]cyclopenta[1″,2″,3″:5′,6′]acenaphtho[1′,2′:5,6]pyrazino[2,3-b]phenazine (1), and two theoretically designed molecules (2 and 3). Compound 2 is formed by substituting i-Pr groups in compound 1 with H atoms, which is designed to evaluate the effect of i-Pr groups on the electron transport properties. Compound 3 is designed by adding one more benzopyrazine group to the conjugation structure of compound 1. It shows that i-Pr group can increase HOMO and LUMO energy levels and improve solubility in organic solvent and hydrophobicity. Enlarging conjugation can not only decrease LUMO energy level and electron reorganisation energy, but also can increase solubility and electron mobility. So our designed compound 3 is expected to be a potential electron transport material in inverted PSCs. [ABSTRACT FROM AUTHOR]

The classical Oseen-Frank theory of liquid crystal elasticity is based on the experimentally verified fact that there are three independent modes of distortion, each with its associated elastic constant. On the other hand, the arguably more first-principles order parameter-based Landau-de Gennes theory only involves two independent elastic modes. The resulting ‘elastic constants problem’ has led to a considerable amount of vexation among theorists. In a series of papers at the turn of the century, Fukuda en Yokoyama suggested that the resolution of this problem could be found in the proper treatment of non-local effects in the ideal part of the free energy. They used an ingenious, but technically complex, technique based on a field-theoretic approach to semi-flexible polymers. Here we revisit their idea but now in the more accessible framework of density functional theory of rigid particles. Our work recovers their main results for rod-like particles, in that generically an ordered assembly of non-interacting rods has three independent elastic constants associated to it that all scale as the square of the length of the particles and obey the inequalities . We also consider the case of disc-like particles, and then find in line with expectations that . [ABSTRACT FROM AUTHOR]

The paper by Nold et al. [Phys. Fluids 26 (7), 072001 (2014)] examined density profiles and the micro-scale structure of an equilibrium three-phase (liquid-vapour-solid) contact line in the immediate vicinity of the wall using elements from the statistical mechanics of classical fluids, namely density-functional theory. The present research note, building on the above work, further contributes to our understanding of the nanoscale structure of a contact line by quantifying the strong dependence of the liquid-vapour density profile on the normal distance to the interface, when compared to the dependence on the vertical distance to the substrate. A recent study by Benet et al. [J. Phys. Chem. C 118 (38), 22079 (2014)] has shown that this could explain the emergence of a film-height-dependent surface tension close to the wall, with implications for the Frumkin-Derjaguin theory. [ABSTRACT FROM AUTHOR]

Lung cancer has received considerable attention in recent years due to its high mortality. The difficulty in awareness of such disease can be attributed to its strong insidiousness during the early stage. Therefore, the prognosis of lung cancer becomes significant so as to nip this disease in the bud. In this paper, the Rh-doped CNT-based biosensors were introduced to realise the diagnosis of lung cancer through detecting the exhaled gas of possible patients. The adsorption property and sensing mechanism of Rh-CNT towards two kinds of mainly typical gases of lung cancer, namely, C6H6 and C6H7N, were analysed based on density functional theory, aiming at evaluating the potential application of such material to be gas sensors. The results indicated that the Rh-CNT not only has good adsorption towards such two gases but also obvious conductivity increase when interacted with any of them, while presents insensitivity upon the common exhaled gas, CO2. We suggest the Rh-CNT be prepared as biosensors applied in the field of lung cancer pre-diagnosis that can be used in our daily life without pain and complex clinical examination. [ABSTRACT FROM AUTHOR]

The paper presents the results of ab initio modelling of the interaction of hydrogen atoms with ferrite/cementite interfaces in steels and thermodynamic assessment of the ability of interfaces to trap hydrogen atoms. Modelling was performed using the density functional theory with generalised gradient approximation (GGA’96), as implemented in WIEN2k package. An Isaichev-type orientation relationship between the two phases was accepted, with a habit plane (101)c∥ (112)α. The supercell contained 64 atoms (56 Fe and 8 C). The calculated formation energies of ferrite/cementite interface were 0.594 J/m2. The calculated trapping energy at cementite interstitial was 0.18 eV, and at the ferrite/cementite interface – 0.30 eV. Considering calculated zero-point energy, the trapping energies at cementite interstitial and ferrite/cementite interface become 0.26 eV and 0.39 eV, respectively. The values are close to other researchers’ data. These results were used to construct a thermodynamic description of ferrite/cementite interface-hydrogen interaction. Absorption calculations using the obtained trapping energy values showed that even thin lamellar ferrite/cementite mixture with an interlamellar spacing smaller than 0.1 μm has noticeable hydrogen trapping ability at a temperature below 400 K. [ABSTRACT FROM AUTHOR]

In this paper, density functional theory method was employed to study the electronic absorption spectrum and electronic static second hyperpolarisability of X-shaped pyrazine derivatives with two-dimensional charge-transfer structures. Computational results show that the push–pull electron abilities of the substituent groups and the length of the conjugated chains affect the electronic spectrum and static second hyperpolarisability of the pyrazine derivatives. As the push–pull electron abilities of the substituent groups or the length of the conjugated chains increases, the frontier molecular orbital energy gap decreases, resulting in increased second hyperpolarisability and redshift of the electronic absorption bands. The electronic absorption spectra of the pyrazine derivatives maintain good transparency in the blue light band. The electronic static second hyperpolarisability exhibits a linear relationship to the frontier molecular orbital energy gap. Particularly, increasing/decreasing the push–pull electron abilities of the substituent groups considerably affect the static second hyperpolarisability in long conjugated systems, which is important to the modulation of molecular organic nonlinear optical (NLO) properties. The studied pyrazine derivatives show large third-order NLO response and good transparency in the blue light band and are thus promising candidates as NLO materials for photonics applications. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the electronic and magnetic properties of Cu-doped nickel clusters by means of density functional theory. The stabilities of these clusters have also been studied in terms of the binding energies, second-order difference of energies, fragmentation energies and HOMO--LUMO energy gaps. The obtained results reveal that the N4Cu, N5Cu and Ni7Cu clusters are found to be more stable that than all other clusters. Higher HOMO--LUMO gap was observed for Ni5Cu cluster (2.265 eV), indicating its higher chemical stability. A half-metallic behaviour has also been observed for the NinCu clusters, which suggests that these clusters can be employed as nanocatalysts for several catalytic processes, particularly for hydrogenation and dehydrogenation reactions. The magnetism calculations show that the magnetic moment is mostly located on the Ni atoms, and the contribution of the Cu atom to the total magnetic moment in the NinCu clusters is very small. Furthermore, partial density of states analysis indicates that the 3d orbitals in Ni atoms are mostly responsible for the magnetic behaviour of these clusters, and the s orbitals have a very little contribution to the total magnetic moment. [ABSTRACT FROM AUTHOR]

The effects of bend angle on the stability, electronic structure and optical properties of Li-absorbed borophene system are studied by using density functional theory based on the first principles. The structure of borophene did not change significantly after adsorption of a Li atom, and the planar structure of borophene was not destroyed. Bending deformation affects the stability of the adsorption system and reduces the binding energy of the adsorption system. The adsorption of Li atoms obviously changes the energy band structure of borophene, and more impurity levels appear in the conduction band. The 2s orbital of Li and the 3p orbital of B are obviously hybridised. A charge transfer occurs between Li atoms and borophene. As the deformation increases, the amount of charge transfer increases. The bending angle affects the size of the absorption peak and reflection peak of the adsorption system. [ABSTRACT FROM AUTHOR]

The present work deals with the understanding of the integrated experimental and theoretical study of the molecular structure and vibrational spectra of N-allyl-N-ethylformamide (NAEF). Density functional theory (DFT) calculations were used to study the subject molecule, N-allyl-N-ethylformamide (NAEF), utilising the B3LYP method and the basis set 6-311++G (d,p). Geometrical parameters and the structure of NAEF were computed such that global descriptors and reactive sites were obtained. Frontier's analysis of molecular orbital energy demonstrates that the molecule's charge exchange is considerably high. Non-linear optical properties of N-allyl-N-ethylformamide (NAEF) were computed and compared with the standard material of urea. The vibrational assignments were analysed for the existence of the probable functional groups and tabulated. The thermodynamic functions were computed at different temperatures and listed accordingly. NMR spectroscopy and quantum computational chemistry methods have been employed for the understanding of the structures of NAEF. Moreover, different techniques such as topological analysis and drug-likeness were utilised to determine the structure and other properties of NAEF. The molecular docking study could determine the residue with the highest docking score (lowest binding energy) and the most non-covalent interactions. [ABSTRACT FROM AUTHOR]

The impact of the active site produced by the active metal V centre on the production of phenol from benzene was deduced from the cluster model structure of VAPO-5. In this work, the mechanism of benzene to phenol under the VAPO-5 model was explored. The transition states, intermediates, and reaction energy barrier throughout the reaction were evaluated by the ONIOM approach, which combines semi-empirical analysis with density functional theory. The outcomes demonstrated that this reaction was divided into four stages, with each stage's energy barriers being 59.9, 122, 204.8, and 60.7 kJ/mol, respectively. And a lower energy barrier of 204.8 kJ/mol must be surpassed to pass the determining speed phase's energy barrier of 296.8 kJ/mol. Additionally, the solvation of acetonitrile was looked into, resulting in the crossing of the energy barrier of 174.8 kJ/mol. [ABSTRACT FROM AUTHOR]

Equilibrium geometries and thermodynamic potentials of the neutral and ionised species of the $ \hbox {Na}\cdots (\hbox {H}_{2}\hbox {O})_{{n}} $ Na ⋯ (H 2 O) n ( $ {n}=1,..,8 $ n = 1 ,.. , 8) mixed clusters were computed at MN15/def2-TZVPD level of density functional theory (DFT). The vertical and adiabatic ionisation energies and enthalpies were computed and their cluster size dependence was discussed. Laser-induced ionisation involves electronic excitation through Rydberg-type excited states, which have been characterised using the TDDFT method, including the ωB2PLYP double-hybrid exchange-correlation functional. Ab initio molecular dynamics calculations were performed on a time scale of 20 picoseconds. Fluctuations of the charge and the sodium–oxygen atomic distances predict that, the $ 3\hbox {s}^{1} $ 3 s 1 electron of the sodium atom are transferred from the delocalised Rydberg orbitals to the Rydberg orbitals around the water molecules and the sodium atom becomes positively charged with around 0.6e after the first $ 10\,\hbox {ps} $ 10 ps . On the other hand, some of the water molecules can move away up to 5 Å from the sodium with a significant negative charge on them. It has been shown that non-radiative relaxation cannot be excluded, they can mostly occur for cases $ n \geqslant 4 $ n ⩾ 4. The results confirm that the adiabatic photo-ionisation can occur on the basis of cluster disintegration. [ABSTRACT FROM AUTHOR]

Approaches and programs for calculations of the EPRg-tensor in the framework of the two- and four-component methods are still very rare. There are three main reasons for this: the wider community's unawareness of the importance of second- and higher order spin–orbit effects on theg-tensor, the methodological problems associated with performing such calculations and the lack of understanding of these problems. This paper reports on the implementation of a method for calculation of theg-tensor in the framework of the relativistic unrestricted two- and four-component Hartree–Fock and density functional theory approaches based on the Kramers pair formalism. This implementation allows us to analyse problems which arise when theg-tensor is calculated via Kramers pairs in the unrestricted framework. [ABSTRACT FROM AUTHOR]

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes. [ABSTRACT FROM AUTHOR]

Based on the first principle, this paper uses the generalised gradient approximation density functional theory and slab model to investigate the dissociation of methane (CH4→CH3 + H) on the surfaces of Co group (Co, Rh, Ir) and Ni group (Ni, Pd, Pt), and investigate the influence of PtIr(100), PdRh(100) and PtPd(100) on methane decomposition. From the calculated activation energies of methane dissociation on single metal surfaces and alloy surfaces,we find that Pt and Ir are better catalysts for methane dissociation in the single metals studied. In addition, methane dissociation (CH4→CH3 + H) on PtIr(100) and PdRh(100) surfaces are easier than that on single metal surfaces(Co, Rh, Ir, Ni, Pd, Pt). [ABSTRACT FROM AUTHOR]

In the heavy metal removal industry, adsorption is a famous and commonplace procedure well-recognized for its flexibility and utility. It is also a cost-effective procedure. Moreover, there are several adsorption procedures that are reversible on the one hand, and adsorbents may be reused after passing different desorption techniques on the other. The foundation of this research is to apply the calculations of the density functional theory (DFT) based on ab initio with an aim to explore the heavy metal atoms' adsorption properties on ZnO–graphene resembling structure sheets and zinc oxide (ZnO) nanotubes. The heavy metals considered in this study include (Cu2+), (Pb2+), (Cd2+), and (Ag2+). In the initial stage, this study optimises both nanostructures. In the next phase, this study computes the steadiest configuration, the energy of adsorption, and the distance of equilibrium for each heavy metal with nanostructures utilising the mentioned DFT method. The findings were analyzed and compared. According to our case-by-case findings, ZnO-nanotubes exhibited better adsorption behaviour than ZnO–graphene sheets due to a smaller distance for equilibrium and higher adsorption energy. we've created the diagrams of the electronic density of states (DOS) in order to analyze the molecule adsorption electrical properties. [ABSTRACT FROM AUTHOR]

Hydrogen that is accumulated within the grain boundaries can lead to a decrease of the critical strain required to fracture the material. The paper presents results ofab initiomodelling of hydrogen–grain boundary interaction in ferromagnetic bcc iron. Modelling was performed using density functional theory with generalised gradient approximation (GGA’96), as implemented in WIEN2k package. Three fully relaxed tilt grain boundaries, Σ5(310), Σ5(210) and Σ3(111), were studied. The supercells contained 40–48 atoms, i.e. 20–24 atoms in each of the two ‘grains’. Calculated formation energies of grain boundaries is 1.44, 1.83 and 1.46 J/m2and the maximum binding (trapping) energies of hydrogen to the boundaries are 0.43, 0.83 and 0.39 eV, respectively. These values are close to other researchers’ data. The higher value of trapping energy of the Σ5(210) boundary is probably due to the asymmetrical atom configurations resulting from mutual rigid shift of the two grains that was necessary to be introduced to provide optimal distances between Fe atoms, unlike the other two boundary types. [ABSTRACT FROM AUTHOR]

Recently, I have derived conditions to characterise the kernel of the retarded response function, under the assumption that the initial state is a ground state. In this paper, I demonstrate its generalisation to mixed states (ensembles). To make the proof work, the weights in the ensemble need to be decreasing for increasing energies of the pure states from which the mixed state is constructed. The resulting conditions are not easy to verify, but under the additional assumptions that the ensemble weights are directly related to the energies and that the full spectrum of the Hamiltonian participates in the ensemble, it is shown that potentials only belong to the kernel of the retarded response function if they commute with the initial Hamiltonian. These additional assumptions are valid for thermodynamic ensembles, which makes this result physically relevant. The conditions on the potentials for the thermodynamic ensembles are much stronger than in the pure state (zero temperature) case, leading to a much less involved kernel when the conditions are applied to the retarded one-body reduced density matrix response function. [ABSTRACT FROM PUBLISHER]

Charge-transfer (CT) excitations are essential for photovoltaic phenomena in organic solar cells. Owing to the complexity of molecular geometries and orbital coupling, a detailed analysis and spatial visualisation of CT processes can be challenging. In this paper, a new detail-oriented visualisation scheme, the particle–hole map (PHM), is applied and explained for the purpose of spatial analysis of excitations in organic molecules. The PHM can be obtained from the output of a time-dependent density-functional theory calculation with negligible additional computational cost, and provides a useful physical picture for understanding the origins and destinations of electrons and holes during an excitation process. As an example, we consider intramolecular CT excitations in Diketopyrrolopyrrole-based molecules, and relate our findings to experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, we have investigated the catalytic mechanism of rat liver arginase using a quantum mechanics/molecular mechanics (QM/MM) approach. The enzyme catalyses the hydrolysis of L-arginine (L-Arg) to generate L-ornithine and urea. The reaction mechanism proposed by the previous experimental studies is well reproduced by the QM/MM computations. The explicit treatment of the protein environment suggests that Glu277 fulfil its role in stabilising and orienting L-Arg before nucleophilic attack by the bridging hydroxide in the first step. We have also found that the proton transfer step involving a hydrogen bond switch is the rate-limiting step. The activation energy is computed to be 9.0 and 5.9 kcal/mol at the UB3LYP-D3/CHARMM22 and UBHandHLYP-D3/CHARMM22 levels, which are comparable to the observed activation barrier of 7.2 kcal/mol. [ABSTRACT FROM AUTHOR]

Can a C60layer cover a surface of single-wall carbon nanotube (SWCNT) forming an exohedral pure-carbon hybrid with only van der Waals interactions? The aim of the present paper is to address this question and to demonstrate that the fullerene shell layer in such a bucky-corn structure can be stable. Theoretical study of the structure, stability and electronic properties of bucky-corn hybrids is reported for the shell of C60and C70molecules on an individual SWCNT, C60dimers on an individual SWCNT as well as C60molecules on SWNT bundles. The geometry and total energies of the bucky-corn hybrids were calculated by the molecular dynamics method, while the density functional theory method was used to simulate the electronic band structures. [ABSTRACT FROM AUTHOR]

In this paper, various implementations of the analytic Hartree–Fock and hybrid density functional energy second derivatives are studied. An approximation-free four-centre implementation is presented, and its accuracy is rigorously analysed in terms of self-consistent field (SCF), coupled-perturbed SCF (CP-SCF) convergence and prescreening criteria. The CP-SCF residual norm convergence threshold turns out to be the most important of these. Final choices of convergence thresholds are made such that an accuracy of the vibrational frequencies of better than 5 cm−1compared to the numerical noise-free results is obtained, even for the highly sensitive low frequencies (<100–200 cm−1). The effects of the choice of numerical grid for density functional exchange–correlation integrations are studied and various weight derivative schemes are analysed in detail. In the second step of the work, approximations are introduced in order to speed up the computation without compromising its accuracy. To this end, the accuracy and efficiency of the resolution of identity approximation for the Coulomb terms and the semi-numerical chain of spheres approximation to the exchange terms are carefully analysed. It is shown that the largest performance improvements are realised if either Hartree–Fock exchange is absent (pure density functionals) and otherwise, if the exchange terms in the CP-SCF step of the calculation are approximated by the COSX method in conjunction with a small integration grid. Default values for all the involved truncation parameters are suggested. For vancomycine (176 atoms and 3593 basis functions), the RIJCOSX Hessian calculation with the B3LYP functional and the def2-TZVP basis set takes ∼3 days using 16 Intel® Xeon® 2.60GHz processors with the COSX algorithm having a net parallelisation scaling of 11.9 which is at least ∼20 times faster than the calculation without the RIJCOSX approximation. [ABSTRACT FROM PUBLISHER]

The electronic structure and spectroscopy of some representative dinuclear compounds containing CpM(CO)3 and CpM(CO)2 groups were studied using TDDFT (Time Dependent Density Functional Theory). These compounds contain Cp (cyclopentadienyl) as a ligand, and M can be Cr, Mo or W. Their main electronic transitions were calculated and the results are in good agreement with the experimental data. This allows the assignment of some bands whose origin was not clear. In all the cases, the carbonyls and Cp groups restrict the symmetry. The molecular orbitals that would be involved in M-M bonding interact strongly with the carbonyls and show unusual shapes and occupations. The strongest electronic bands are caused by σ→σ* transitions in most of the molecules containing CpM(CO)3 groups, whereas in molecules such as Cp(CO)2M≡M(CO)2Cp the most intense bands are produced by π→π* transitions. The origin of other bands is now explained. The effect of the solvent on the electronic transitions and the use of EOM-CCSD method in some compounds were also checked. [ABSTRACT FROM AUTHOR]

Density functional theory and the non-equilibrium Green's function are combined to investigate the co-modulation effect of endohedral Au atom and anchor S atoms on C 20 . In this paper, anchor atoms Au and S are used, respectively, to connect the endohedral fullerene C 20 with Au nanowires, respectively. Both density of states and transmission coefficient as functions of energy and voltage are investigated to evaluate the spin interaction between molecular orbital and itinerant electrons and explain the influence on current–voltage dependence of C 20 . The results show that different combination of endohedral and anchor atoms can promote or inhibit the transmission probability of itinerant electrons. Co-modulation cannot only present more abundant transmission properties but also form spin asymmetric transmission peaks that may perform new nano circuit functions. [ABSTRACT FROM AUTHOR]

Stimulated by agricultural development, ammonia becomes the second buck chemical in the world, and many ammonia synthesis plants will discharge ammonia-containing wastewater and destroy the ecological balance. In this work, Density Functional Theory (DFT) method was used to study the adsorption characteristic of typical aliphatic boranes on NH3 as well as N2, H2 and CH4. The results showed that the adsorbents could selectively adsorb NH3 over N2, H2 and CH4. The chain length of CH2 has little effect on the adsorption characteristic of boranes while the adsorption energy strongly affected by the number of CH3 groups directly attached to B for boranes. The analysis of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) indicated that LUMO is contributed by adsorbent and HOMO is contributed by adsorbate. Molecular electrostatic potential indicated that the positive charge of B and the negative charge of N can form the optimal configuration. The selectivity coefficient showed that the adsorbent has high selectivity to ammonia. The desorption of NH3 could be readily achieved by increasing temperature. This study can provide the adsorption mechanism of this system and give a guidance on designing reusable aliphatic borane resin to selectively adsorb and recover NH3. [ABSTRACT FROM AUTHOR]

The role of H atoms in the formation of irradiation-induced He bubbles in SiC grain boundaries (GBs) is unclear. The effects of H on the formation energies (Efs) and diffusion behaviour of He in the 3C-SiC twin boundary (TB) were studied using the density functional theory. We observed that a He atom stabilises at three typical sites in the 3C-SiC (310) TB with Efs = 1.95, 2.05, and 1.67 eV, which are significantly lower than those in the SiC grains. The addition of the H atom shifts the stable sites of He in the TB and increases Efs to 4.66, 3.96, and 5.13 eV. The minimum energy pathways for He diffusion in TB were changed by the addition of H atom. Moreover, the H atom reduces the barrier from 3.69 to 1.04 eV for the He diffusion in one TB void and increases it from 1.30 to 4.08 eV for the He diffusion between adjacent TB voids. We interpreted the above results through the Bader charge, density of states, and atomic force analysis. The results indicate that H promotes the in-void diffusion but suppresses the inter-void diffusion of He atoms in SiC GBs, which favours the aggregation and nucleation of He in SiC GBs. [ABSTRACT FROM AUTHOR]

In this paper we show how it is possible to obtain the pKaof a weak acid (H4SiO4) bound to a highly charged cation (La3+) from DFT-based molecular dynamics in a relatively simple, tunable and efficient way. This was done by combining molecular dynamics in bulk water of a La3+/H4SiO4complex with the single sweep method. At this end, we have first performed molecular dynamics runs where a high temperature is assigned on the defined reaction coordinate, here the O–H distance. Then we performed constrained molecular dynamics simulations for selected values of the reaction coordinate along the observed dissociation pathway. The average forces obtained from those constrained simulations are then interpolated to get a final free energy curve. The pKais obtained by integrating the resulting free energy curve and that of a reference calculation, the autodissociation of water. We then show that the pKaof the silanol groups away from La3+is close to the first pKaof silisic acid, while the pKaof the silanol groups interacting with La3+is about three units lower. [ABSTRACT FROM AUTHOR]

In the present paper, we have used density functional theory to study electronic properties of bilayer graphene and graphyne doped with B and N impurities in the presence of electric field. It has been demonstrated that a band gap is opened in the band structures of the bilayer graphene and graphyne by B and N doping. We have also investigated influence of electric field on the electronic properties of BN-doped bilayer graphene and graphyne. It is found that the band gaps induced by B and N impurities are increased by applying electric field. Our results reveal that doping with B and N, and applying electric field are an effective method to open and control a band gap which is useful to design carbon-based next-generation electronic devices. [ABSTRACT FROM AUTHOR]

Hydrogen bonding is one of the most important and ubiquitous interactions present in Nature. Several studies have attempted to characterise and understand the nature of this very basic interaction. These include both experimental and theoretical investigations of different types of chemical compounds, as well as systems subjected to high pressure. The O–H..O bond is of course the best studied hydrogen bond, and most studies have concentrated on intermolecular hydrogen bonding in solids and liquids. In this paper, we analyse and characterise normal hydrogen bonding of the general type, D–H...A, in intramolecular hydrogen bonding interactions. Using a first-principles density functional theory approach, we investigate low energy conformers of the twenty α-amino acids. Within these conformers, several different types of intramolecular hydrogen bonds are identified. The hydrogen bond within a given conformer occurs between two molecular groups, either both within the backbone itself, or one in the backbone and one in the side chain. In a few conformers, more than one (type of) hydrogen bond is seen to occur. Interestingly, the strength of the hydrogen bonds in the amino acids spans quite a large range, from weak to strong. The signature of hydrogen bonding in these molecules, as reflected in their theoretical vibrational spectra, is analysed. With the new first-principles data from 51 hydrogen bonds, various parameters relating to the hydrogen bond, such as hydrogen bond length, hydrogen bond angle, bond length and vibrational frequencies are studied. Interestingly, the correlation between these parameters in these bonds is found to be in consonance with those obtained in earlier experimental studies of normal hydrogen bonds on vastly different systems. Our study provides some of the most detailed first-principles support, and the first involving vibrational frequencies, for the universality of hydrogen bond correlations in materials. [ABSTRACT FROM AUTHOR]

Spectroscopic observables can be used for monitoring relaxation processes of molecules. In particular, electron spin resonance of stable multi-radicals is sensitive to the details of the rotational and internal dynamics in rigid and flexible molecules. Integration with advanced theoretical/computational methods proves to be particularly effective to acquire direct information on long-range relaxation processes, based on molecular dynamics, multi-scale approaches and coarse-graining treatments. Together, experimental data and computational interpretation provide a way to understand the effect of chemical changes on specific systems. In this paper we review computational tools aimed at the characterisation of dynamical properties of molecules gathered from electron spin resonance measurements. Stochastic models are employed, based on a number of structural parameters that are calculated at atomistic and/or mesoscopic level depending on their nature. Open source software tools built as user-friendly ‘virtual spectroscopes’ targeted for use by experimentalists are provided as a kind of extension of the laboratory equipment. An overview of their range of applicability is provided. [ABSTRACT FROM PUBLISHER]

For a molecule with a complicated electronic structure, the solution of the Kohn–Sham equations of density functional theory (DFT) may require the use of an ensemble density matrix rather than a pure-state density matrix. In this paper, we first outline how an ensemble density matrix may be parameterised in a form, which ensures that all occupation numbers are between zero and two and that the total number of electrons is constant. A previously developed method for the optimisation of both orbitals and occupation numbers is summarised, and a time-independent linear response method for ensemble densities is developed. The optimisation and linear response methods are applied to the energy, dipole moment and static polarisability of the ground state of ozone at various bond angles. When comparing the results of pure-state and ensemble DFT calculations, it is found that the latter gives better agreement with wave-function methods and in particular provides smooth and differentiable potential and property curves. [ABSTRACT FROM AUTHOR]