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CH $_3$ internal rotation is one of the typical large amplitude motions in polyatomic molecules, the spectral analysis and theoretical calculations of which, were developed by Li-Hong Xu and Jon Hougen. We observed a Doppler-free high-resolution and high-precision spectrum of 9-methylanthracene (9MA) by using the collimated supersonic jet and optical frequency comb techniques. The potential energy curve of CH $_3$ internal rotation is expressed by a six-fold symmetric sinusoidal function. It was previously shown that the barrier height ( $V_6$ ) of 9MA- $d_{12}$ was considerably smaller than that of 9MA- $h_{12}$ [M. Baba, et al., J. Phys. Chem. A 113, 2366 (2009)]. We performed ab initio theoretical calculations of the multi-component molecular orbital method. The barrier reduction by deuterium substitution was partly attributed to the difference between the wave functions of H and D atomic nuclei.

The A–X transition of diatomic bismuth, Bi2, was revisited by laser induced fluorescence in solid Ne at 3 K. Molecular constants, i.e., vibrational frequencies of 137 cm–1 and 174 cm–1, were reproduced for the upper and lower electronic states as reported by Bondybey et al. [Chem. Phys. Lett. 76, 30 (1980)]. Two-dimensional mapping of emission spectra confirmed satellite bands in higher and lower excitation/emission energies for each of the major bands in the vibrational progression of v′–v″ (v′ = 0–5, v″ = 5–12). Based on the molecular orbital calculations, presence of clusters, Bi2Nen (n = 1–6), is proposed for possible carriers of the observed satellites. For the relatively large matrix shift of ∼67 cm−1 in solid Ne for the term energy of the A state, the diatomic bismuth is supposed to exist as a linearly coordinated cluster of Bi2Ne in the matrix.

We report on results of first-principles density-functional theory (DFT) calculations of energy levels of molecular orbitals (MO) and results of electronic excitation spectra calculations performed using Tamm-Dancoff approximation (TDA) to time- dependent density functional theory (TDDFT) of graphene quantum dots (GQDs) with edge functionalization. Polyciclic aromatic hydrocarbon models of GQDs functionalized with oxide and amine groups -OH, -COOH, -COH, NH2 were considered. The calculation results showed that with an increase in the diameter of the GQDs ELUMO-EHOMO decreases, the oxide groups -COOH, -COH shift these levels lower relative to the energy levels of the GQDs passivated by the -H atom due to the withdrawal of electrons from the graphene skeleton. The calculated electronic excitation spectra were compared with the UV- Vis spectra of hydrothermally synthesized carbon quantum dots. Comparison of the calculation results and experimental spectra shows a qualitative agreement, which make it is possible to suggest that the considered disk-shaped models of GQDs (coronene and C54H18 molecules) can be basic absorbing structures of the GQDs or carbon quantum dots.

The canonical molecular orbitals (CMO) calculation provides useful knowledge such as molecular orbitals, energy level, charge density and so on. As one of the properties obtained from the CMO calculation of protein results, the interaction energy analysis between amino acid residues and/or substrates is useful as molecular design and functional analysis. The energy decomposition analysis approaches are the well-known calculation methods for interaction energy analysis, however, the electronic structure calculation of large molecule is very expensive and hard to achieve. Therefore, we have implemented the interaction analysis method by using the energy density analysis (EDA) method. The calculation for the EDA method is as simple as the Mulliken population method but requires matrix elements for energy calculation. By adopting the grid-free method for the exchange-correlation term, we could apply the EDA method in the DFT scheme.

4,5-dihydro-1H-pyrazol this series, was synthesizing usage of this reaction. Certain compounds commonly prepared for the cyclization of chalcone with hydrazine derivatives undergoing the alcoholic conditions. Meanwhile the theoretical calculations based on density functional theory (DFT) used to B3LYP level. The molecular geometry in frontier molecular orbital and mulliken charge of this compound were established to give an excellent perception of molecular properties. The molecular electrostatic potential of compound was as certain to inhibit like electrophilic or neuclephilic reactivity. The result get disclose a quality accord linking to the theoretical capitalize.

In this computational investigation on 4-(2-Oxo-2H-benzo[h]chromen-4-ylmethoxy)-benzaldehyde benzofuran derivative, the compound is initially optimized to get the clear structure,then it is used for further investigation. The highest occupied molecular orbitals, lowest unoccupied molecular orbitals, theoretical bandgap energy, electrostatic potential map such as total electron density and molecular electrostatic potential map were estimated at the ground state. From the molecular orbital structure, the HOMO value is found to be E=-7.119 eV and the LUMO value is found to be E= -4.999 eV, In view of that, bandgap energy is found to have 2.35 eV in the ground state. The electrostatic potential maps in both the cases revealed the compound showed the most electronegative site at oxygen attached group of the titled benzofuran derivative and showed nucleophilic site at 9C, 10C, 11C, 12C, 14C, 15C, and 18C atoms of the benzofuran derivative.

The molecular structure of the 1,4-Bis(methylamino)anthraquinone molecule was optimized by the DFT/B3LYP method with 6-311G++(d,p) basis set using Gaussian 09 program. The vibrational frequencies were assigned on the basis of potential energy distribution calculation using VEDA 4.0 program. The 1H and13C NMR isotropic chemical shift values of the molecule were calculated using Gauge-Invariant-atomic orbital method in DMSO solution. The UV-Visible spectrum of the molecule was simulated by the time dependent-DFT/B3LYP method associated with the polarizable continuum model using 6-31G++ (d.p) basis set using ethanol as the solvent. The molecular reactivity and kinetic stability of the molecule were confirmed using frontier molecular orbitals analysis. The Mulliken atomic charge distribution values of the molecule were calculated. The natural bond orbital analysis was performed to evaluate the donor-acceptor interactions within the molecule. The molecular docking analysis confirms that the title molecule acts as a good inhibitor of the protein kinase CK2, which is used as a molecular target in a preclinical in vitro model of pancreatic cancer. Hence, the present study paves the way for designing the novel drugs for the treatment of pancreatic cancer.

Here in, we report the theoretical investigation of the anisotropic charge transport property of the p-type compound, 5,5’-bis(pyren-2-yl)-2,2’-bithiophene (BPBT) organic crystalusing Marcus-Huss theory at density functional theory (DFT) level. The planar geometry and delocalized frontier molecular orbitals of BPBT indicate acceptable molecular stacking and good electronic properties of the compound. The energy level of the highest occupied molecular orbital (HOMO) was found to be -5.357 eV, which indicated better air stability of BTBT. The computed low reorganization energies (hole/electron; λh/λe = 0.235/0.234 eV respectively) andhigh anisotropic hole mobility (3.431 cm2V−1s−1)of BPBT inferredthe fact that the compound could beused as a potential p-type organic semiconductor.

Membrane is the most important component in Proton Exchange Membrane Fuel Cell (PEMFC) which is widely developed in recent years. One of the membranes used in the PEMFCs is N-carboxymethyl chitosan. The aim of this research is to identify the possibility of intermolecular hydrogen bond interactions in N-carboxymethyl chitosan and nH2O (n=1-5) by using density functional theory to perform all the calculations. In this letter, we report all the possibility of hydrogen bond interactions by analyzing natural bond orbital to measure the relative strength of the hydrogen bonding interactions and the charge transfer of n-σ* from O-H. Interaction of N-carboxymethyl chitosan and 5H2O was found to be the strongest hydrogen bond among others with a stabilization energy of 56.93 kcal/mol. The value of stabilization energy was confirmed using molecular orbital calculation. Hydrogen bond interaction was predicted influenced by existing of the carboxylic group.

An organometallic compound, guanidine chromate was synthesized adopting solvent evaporation method. The present work covers the synthesis, structural characterization by experimental single crystal XRD. In addition, theoretical calculations were carried out to find the molecular geometry, HOMO-LUMO energy, ionization potential, chemical hardness and chemical potential for the title compound using DFT method. Natural bonding orbital analysis provides a convenient basis for the investigation of charge transfer, conjugative and hyper-conjugative interactions in the molecular system. The charge distribution within the crystal was studied using dielectric measurement. Result at four different frequencies indicates a decrease in dielectric and conductivity parameters with the increase of temperature at all frequencies.

The search for corrosion inhibitors based on natural products that are environmentally friendly with high inhibition efficiency is still the focus of current research. The corrosion inhibition efficiency of nicotine and its derivatives has been studied using DFT and ab initio MP2 method. This research focuses on the use of electronic parameters and the natural bond analysis approach to explain the corrosion inhibition performance of nicotine and its derivatives. The electronic properties of molecules, including the frontier molecular orbitals (HOMO and LUMO energy), ionization potential, electron affinity, electronegativity, number of electron transfer from inhibitors to metal and interaction energy have a strong relationship with inhibition performance. Interaction mechanism is obtained from natural bond between inhibitors with iron metal in more detail. The presence of electron donor groups within the framework of inhibitors show significant contribution toward the corrosion inhibition performance.

In this present work the theoretical analysis of 3,3’-(naphthalen-2-ylmethylene) bis (4-hydroxy-2H-chromen-2-one) coumarin derivative have been explained. The molecule was optimized in gas phase by keeping Density Functional Theory-Becke’s 3 Lee-Yang-Parr/6-311(d) (DFT-B3LYP/6-311(d)) basic set, the frontier molecular orbital in one of the polar solvent vizoctanol have been calculated and the energy gap is found to be 2.96 eV, this indicates that the molecule have good stability and large chemical hardness. Also the molecular structure and electronic structure of the titled derivative have been studied, the molecular electrostatic potential map, spin electron density of the molecule have been studied, and the electrostatic potential maps was also studied in detail to understand the nucleophilic and electrophilic substituent groups present in the titled molecule. The theoretical parameters such as the electronegativity, chemical potential, hardness, electrophilicity, and softness of the title molecule is derived by using the energy band gap values

Nucleus-independent chemical shift (NICS) data were used to determine the aromaticity of the studied compounds. The influences of substituent type and position on the aromaticity of some derivatives of imidazole, 2- phenylimidazole, benzimidazole and 2-phenylbenzimidazole have been studied theoretically by DFT levels at B3LYP/6- 31+G* and B3LYP/6-311++G** methods. The studied compounds were optimized at the B3LYP/6-31+G* level. We have analyzed the aromaticities of these compounds with the substituents -CH3, -C2H5, -CH(CH3)2, -C(CH3)3, -OH, -OCH3, -NO2, -CN, -F, -Cl and -Br. The most efficient substitution to enhance the aromaticities was calculated to be at positions 5, 7 and ortho position for the studied compounds. The frontier molecular orbital energies (HOMO and LUMO) of the studied compounds were also calculated.

Slow evaporation solution growth method is adopted to grow N-Methylglycine single crystal, which belongs to orthorhombic system with its acentric space group (P212121). In this present work Quantum chemical calculations such as molecular structure optimization, Mulliken atomic charge distribution, frontier molecular orbitals, Molecular electrostatic potential map and first hyperpolarizability calculations were performed using density functional theory to probe its relationship between the structure and property which shows the potential candidature towards NLO applications.

In the present study, we have taken pyridine-based boronic acid as carbohydrate sensor and subjected to understand the sensing and binding properties by virtue of theoretical (DFT and TD-DFT) and experimental (spectrofluorometry) Techniques. Physiochemical parameters were calculated by performing frontier molecular orbital (FMO) analysis. Further, excited states were calculated by implementing TD-DFT method and these excited state properties were compared with the experimental absorption spectra. The (6-fluoropyridin-3-yl)boronic acid (BA2) compound has been tested for sugar sensing application by fluorescence emission spectroscopic analysis, to understand the binding ability of BA2 with sugars (D-glucose and D-fructose). The association and dissociation constants were calculated by employing Stern-Volmer equation. The Job's plot analysis was carried to know the stoichiometry ratio of binding. The Photophysical properties, such as quantum yield and fluorescence lifetime of BA2 and BA2 with sugars were obtained by using PhotochemCAD. The above analysis and the results suggests that BA2 can be a possible candidate for sugar sensing.

Dissociation of molecular hydrogen (H2) is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H2 dissociation by Au1-doped closed-shell titanium oxide cluster anions AuTi3O7− and AuTi3O8− has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and mass-selected to react with H2 in an ion trap reactor. In the reaction of AuTi3O8− with H2, the ion pair Au+−O22− rather than Au+−O2− is the active site to promote H2 dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H2 dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H2 activation and dissociation.

First-principles calculations are applied for investigating influence of electron donating ability of donor groups in eight thermally activated delayed fluorescence (TADF) molecules on their geometrical structures and transition properties as well as reverse intersystem crossing (RISC) processes. Results show that the diphenylamine substitution in the donor part can slightly change the bond angle but decrease bond length between donor and acceptor unit except for the lowest triplet state (T $_1$ ) of carbazole-xanthone molecule. As the electron donating ability of donor groups is increased, the overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is decreased. As the diphenylamine groups are added in donor part, the delocalization of HOMO is enlarged, which brings a decreased energy gap ( $\Delta E$ $_{\text{S}_1\text{-T}_1}$ ) between the lowest singlet excited state (S $_1$ ) and T $_1$ state. Furthermore, with the calculated spin-orbit coupling coefficient ( $H_{\text{so}}$ ), one finds that the larger value of $\displaystyle{\frac{\langle S_1|\hat{H}_{\text{so}}|{T}_1\rangle^2}{\Delta E_{\text{S}_1\text{-T}_1}^2}}$ is, the faster the RISC is. The results show that all investigated molecules are promising candidates as TADF molecules. Overall, a wise molecular design strategy for TADF molecules, in which a small $\Delta E_{\text{S}_1\text{-T}_1}$ can be achieved by enlarging the delocalization of frontier molecular orbitals with large separation between HOMO and LUMO, is proposed.

Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide (CO) and carbon dioxide (CO2) in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×1013 W/cm2 to 2×1014 W/cm2 using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton (Kr), which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization (NSDI) of CO, while the NSDI probability of CO2 is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules (N2 and O2), the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO2 leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization.

Methanol/TiO2(110) is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the valence band maximum of TiO2, preventing the hole transfer. To study the level alignment of this system, electronic structure of methanol covered TiO2(110) surface has been measured by ultraviolet photoelectron spectroscopy and the molecular orbitals of adsorbed methanol have been clearly identified. The results indicate the weak interaction between methanol and TiO2 substrate. The static electronic structure also suggests the mismatch of the energy levels. These static experiments have been performed without band gap excitation which is the prerequisite of a photocatalytic process. Future study of the transient electronic structure using time-resolved UPS has also been discussed.

The list of σ-hole bonds is long and growing, encompassing both H-bonds and its closely related halogen, chalcogen, etc., sisters. These bonds rely on the asymmetric distribution of electron density, whose depletion along the extension of a covalent bond leaves a positive region of electrostatic potential from which these bonds derive their name. However, the density distributions of other molecules contain analogous positive regions that lie out of the molecular plane known as π-holes, which are likewise capable of engaging in noncovalent bonds. Quantum calculations are applied to study such π-hole bonds that involve linear molecules, whose positive region is a circular belt surrounding the molecule, rather than the more restricted area of a σ-hole. These bonds are examined in terms of their most fundamental elements arising from the spatial dispositions of their relevant molecular orbitals and the π-holes in both the total electron density and the electrostatic potential to which they lead. Systems examined comprise tetrel, chalcogen, aerogen, and triel bonds, as well as those involving group II elements, with atoms drawn from various rows of the Periodic Table. The π-hole bonds established by linear molecules tend to be weaker than those of comparable planar systems.

In this work, we investigate the electronic properties and thermoelectric performance of triangulene π-dimer junctions with the twist angle from 0° to 60° by using first-principles calculations in combination with a non-equilibrium Green's function method. It is found that the triangulene π-dimer can be transformed between nonmagnetic state and antiferromagnetic or ferromagnetic state by varying the twist angle. The reason is that the relative rotation between the monomers weakens the overlap of two single occupied molecular orbital. More importantly, our theoretical analysis shows that the ferromagnetic states of the triangulene π-dimer junctions at the twist angle of 20°, 30°, and 60° have outstanding thermoelectric performance. The corresponding ZT value is as high as around 6, which is mainly contributed from the spin splitting nature. This work is instructive to improve the thermoelectric properties of π-stacking molecular junctions or organic polymers.

Picene, which attracts the great interest of researchers, not only can be used to fabricate thin film transistors with high hole mobilities, but also is the parent material of a new type organic superconductor. Here, we investigate the electronic properties of individual picene molecules directly adsorbed on Cu(111) surface by a combination of experimental scanning tunneling microscopy/spectroscopy measurements and theoretical calculations based on the density functional theory. At low coverage, the picene molecules exhibit mono-dispersed adsorption behavior with the benzene ring planes parallel to the surface. The highest occupied state around −1.2 V and the lowest unoccupied state around 1.6 V with an obvious energy gap of the singly adsorbed picene molecule are identified by the dI/dV spectra and maps. In addition, we observe the strong dependence of the dI/dV signal of the unoccupied states on the intramolecular positions. Our first-principles calculations reproduce the above experimental results and ...

The outer-valence binding energy spectra of ethanol in the energy range of 9–21 eV are measured by a high-resolution electron momentum spectrometer at an impact energy of 2.5 keV plus the binding energy. The electron momentum distributions for the ionization peaks corresponding to the outer-valence orbitals are obtained by deconvoluting a series of azimuthal angular correlated binding energy spectra. Comparison is made with the theoretical calculations for two conformers, trans and gauche, coexisting in the gas phase of ethanol at the level of B3LYP density functional theory with aug-cc-pVTZ basis sets. It is found that the measured electron momentum distributions for the peaks at 14.5 and 15.2 eV are in good agreement with the theoretical electron momentum distributions for the molecular orbitals of individual conformers (i.e., 8a′ of trans and 9a of gauche), but not in accordance with the thermally averaged ones. It demonstrates that the high-resolution electron momentum spectrometer, by inspecting the ...

Manganese-phthalocyanines form assembled chains with a variety of ordered super-structures, flat lying along the Au(110) reconstructed channels. The chains first give rise to a ×5 symmetry reconstruction, while further deposition of MnPc leads to a ×7 periodicity at the completion of the first single layer. A net polarization with the formation of an interface dipole is mainly due to the molecular π-states located on the macrocycles pyrrole rings, while the central metal ion induces a reduction in the polarization, whose amount is related to the Mn-Au interaction. The adsorption-induced interface polarization is compared to other 3d-metal phthalocyanines, to unravel the role of the central metal atom configuration in the interaction process of the d-states. The MnPc adsorption on Au(110) induces the re-hybridization of the electronic states localized on the central metal atom, promoting a charge redistribution of the molecular orbitals of the MnPc molecules. The molecule-substrate interaction is controlled by a symmetry-determined mixing between the electronic states, involving also the molecular empty orbitals with d character hybridized with the nitrogen atoms of the pyrrole ring, as deduced by photoemission and X-ray absorption spectroscopy exploiting light polarization. The symmetry-determined mixing between the electronic states of the Mn metal center and of the Au substrate induces a density of states close to the Fermi level for the ×5 phase.

Novel compounds of the pyridine-imidazole with benzaldehyde and fluoro substituents, methyl attached on the pyridine ring are synthesized and characterized. The structural depiction was performed by FT-IR, 1H & 13C NMR and Mass spectra were recorded. Here we also used DFT results in order to investigate the optoelectronic properties. The optimized geometrical parameters were in good conformity with the corresponding literature values. The NBO analysis using the hyperconjugation interaction energy (E(2)) and electron densities of the donor (i) and acceptor (j) bonds were studied. In addition, Mulliken atomic charges, frontier molecular orbitals, and molecular electrostatic potential were computed by using DFT (DFT/B3LYP) 6-31G (d, p) basis set. The calculated HOMO and LUMO energies illustrate that charge transfer occurs within the molecule.Novel compounds of the pyridine-imidazole with benzaldehyde and fluoro substituents, methyl attached on the pyridine ring are synthesized and characterized. The structural depiction was performed by FT-IR, 1H & 13C NMR and Mass spectra were recorded. Here we also used DFT results in order to investigate the optoelectronic properties. The optimized geometrical parameters were in good conformity with the corresponding literature values. The NBO analysis using the hyperconjugation interaction energy (E(2)) and electron densities of the donor (i) and acceptor (j) bonds were studied. In addition, Mulliken atomic charges, frontier molecular orbitals, and molecular electrostatic potential were computed by using DFT (DFT/B3LYP) 6-31G (d, p) basis set. The calculated HOMO and LUMO energies illustrate that charge transfer occurs within the molecule.

Although canonical molecular orbital (CMO) calculations for proteins are very useful for protein engineering, they are computationally expensive and difficult to achieve because proteins are large molecules. We had developed the third-generation density functional (3G DF) method, which performed electronic state calculation with high efficiency in parallel computer by performing only matrix operation during the SCF calculation. In this study, by applying the powerful computing platform of graphic processing unit (GPU) to our 3G DF calculation method, we constructed a computing environment that achieved the large-scale CMO computation with high efficiency.Although canonical molecular orbital (CMO) calculations for proteins are very useful for protein engineering, they are computationally expensive and difficult to achieve because proteins are large molecules. We had developed the third-generation density functional (3G DF) method, which performed electronic state calculation with high efficiency in parallel computer by performing only matrix operation during the SCF calculation. In this study, by applying the powerful computing platform of graphic processing unit (GPU) to our 3G DF calculation method, we constructed a computing environment that achieved the large-scale CMO computation with high efficiency.

The theoretical investigation of molecular structure of cocrystal, salt and monohydrated salt of chloranilic acid as an electron acceptor with different donors such as 4-aminoaniline, 2-picolinic acid and 2-aminopyrimidine have been performed with the help of DFT/B3LYP/6-311G(d,p) level of theory. The deviations from experimental findings have also been discussed. The frontier molecular orbital analysis has been performed for the determination of band gap as well as charge delocalization.

From our previous molecular orbital calculations using hybrid density functional theory for proton-conducting perovskite metal oxides, it was found that proton pumping effect is combined during proton-conduction, and covalent bonding change occurs in a diagonal line. It is known that pure perovskite metal oxides are regarded as boundary system. It is because they consist of the same unit structures. However, during proton-conduction, both local structural relaxation and local chemical bonding change must be taken into consideration. In this paper, the proton-conducting mechanism is explained from the different viewpoints of local structural relaxation and local chemical bonding change.From our previous molecular orbital calculations using hybrid density functional theory for proton-conducting perovskite metal oxides, it was found that proton pumping effect is combined during proton-conduction, and covalent bonding change occurs in a diagonal line. It is known that pure perovskite metal oxides are regarded as boundary system. It is because they consist of the same unit structures. However, during proton-conduction, both local structural relaxation and local chemical bonding change must be taken into consideration. In this paper, the proton-conducting mechanism is explained from the different viewpoints of local structural relaxation and local chemical bonding change.

In this study, Density Functional Theory (DFT) calculations were conducted on Acyclovir (ACV) hydrate molecular system with the chemical formula of 3[C8H11N5O3]·2[H2O]. Geometry optimization calculations were performed to find the equilibrium structure of 3[C8H11N5O3]·2[H2O]. The optimized geometries were used to find the electronic structures of title molecule, i.e. total energies, frontier molecular orbital energies, atomic charges, and others. The results show that all structural parameters obtained are close to that of experiment. The total energies of 3[C8H11N5O3]·2[H2O] are −70355.92 eV and −70373.84 eV, respectively for DFT/B3LYP/6-31G** and DFT/B3LYP/6-311G** levels of calculations. Using the scheme of Mulliken population analysis (MPA), the highest positive charge was localised on the atom of C12, while for natural atomic charge distribution, C9 atom possesses the highest positive charge. Moreover, the results of vibrational frequencies computed with two different basis sets are close to each other. The computed vibrational frequencies are overall corresponded with the region in the literature studies.In this study, Density Functional Theory (DFT) calculations were conducted on Acyclovir (ACV) hydrate molecular system with the chemical formula of 3[C8H11N5O3]·2[H2O]. Geometry optimization calculations were performed to find the equilibrium structure of 3[C8H11N5O3]·2[H2O]. The optimized geometries were used to find the electronic structures of title molecule, i.e. total energies, frontier molecular orbital energies, atomic charges, and others. The results show that all structural parameters obtained are close to that of experiment. The total energies of 3[C8H11N5O3]·2[H2O] are −70355.92 eV and −70373.84 eV, respectively for DFT/B3LYP/6-31G** and DFT/B3LYP/6-311G** levels of calculations. Using the scheme of Mulliken population analysis (MPA), the highest positive charge was localised on the atom of C12, while for natural atomic charge distribution, C9 atom possesses the highest positive charge. Moreover, the results of vibrational frequencies computed with two different basis sets are close to each oth...

In the present work, we performed a computational investigation of the photoisomerization of spiro[1,3-dihydroindole-2,2′-chromene] [spiropyran (SP)] to merocyanine. The electronic energies and wavefunctions were obtained from configuration interaction calculations, using the floating occupation molecular orbital method, in a semiempirical framework. The parameters of the semiempirical Hamiltonian were re-optimized to reproduce ab initio literature data for SP. In our dynamics simulations, we considered, besides S0, the excited states S1, S2, and S3, which are very close in energy in the Franck–Condon region. We obtained a singlet lifetime of 0.67 ps, in line with the experimental results. We found the photoisomerization quantum yield to depend on the electronic state initially populated.

The photoreduction of a Keggin type lacunary tungstomolybdophosphate, α-(Bu4N)4[H3PW9Mo2O39], in acetonitrile, led to the formation of a monoreduced lacunary heteropoly anion, or a one electron reduced "heteropoly blue" species, whereby the added "blue" electron was captured by the molybdenum atoms. The magnetic properties and behavior of the "blue" electron were studied by a modified Evans nuclear magnetic resonance method (small downshift of the 31P signal) and variable-temperature electron paramagnetic resonance (g = 1.936 for MoV). The intermolecular exchange of the "blue" electron was limited by a geometrical factor, which requires the contact between Mo caps to exchange it between the heteropoly couple. The intramolecular exchange of the "blue" electron between Mo atoms was rather fast (5.3 × 109 s-1), with a rate of more than six orders of magnitude larger than the intermolecular exchange rate. Density functional theory was used to determine the most prevalent protonation sites in the mixed lacunary isomers with the aim of studying the intramolecular electron transfer pathway in the isolated [H4PW9Mo2O39]4- species. The singly occupied molecular orbital (SOMO) is essentially localized in one of the two nonequivalent molybdenum sites. The kinetics of the intramolecular electron exchange equilibrium MoV + MoVI → MoVI + MoV between the two molybdenum atoms bridged by an oxygen atom was found to be fast in agreement with the experimental result. The transition state is of mixed-valence type, with the SOMO delocalized over the Mo-O-Mo group. Spectroscopic parameters were found to be in fair agreement with experimental results.

Valence photoelectron spectra and photoelectron angular distributions of trans-dichloroethene have been measured with vibrational resolution at photon energies between 19 eV and 90 eV. Calculations of photoelectron anisotropy parameters, β, and harmonic vibrational modes help provide initial insight into the molecular structure. The photon energy range encompasses the expected position of the atomic Cl 3p Cooper minimum. A corresponding dip observed here in the anisotropy of certain photoelectron bands permits the identification and characterization of those molecular orbitals that retain a localized atomic Cl character. The adiabatic approximation holds for the X 2Au state photoelectron band, but vibronic coupling was inferred within the A–B–C and the D–E states by noting various failures of the Franck–Condon model, including vibrationally dependent β-parameters. This is further explored using the linear vibronic coupling model with interaction parameters obtained from ab initio calculations. The A/B photoelectron band is appreciably affected by vibronic coupling, owing to the low-lying conical intersection of the A 2Ag and B 2Bu states. The C 2Bg band is also affected, but to a lesser extent. The adiabatic minima of the D 2Au and E 2Ag states are almost degenerate, and the vibronic interaction between these states is considerable. The potential energy surface of the D 2Au state is predicted to have a double-minimum shape with respect to the au deformations of the molecular structure. The irregular vibrational structure of the resulting single photoelectron band reflects the non-adiabatic nuclear dynamics occurring on the two coupled potential energy surfaces above the energy of their conical intersection.

Electrochromic devices offer many technological applications, including flexible displays, dimmable mirrors, and energy-efficient windows. Additionally, adsorbing electrochromic molecular assemblies onto mesoporous metal-oxide surfaces facilitates commercial and manufacturing potential (i.e., screen-printing and/or roll-to-roll processing). These systems also demonstrate synthetic versatility, thus making a wide array of colors accessible. In this work, using Time-Dependent Density Functional Theory (TD-DFT), we investigated ten different bi-aryl type molecules of 3,4-ethylendioxythiophene (EDOT) conjugated to various phenyl derivatives as potential anodically coloring electrochromes (ACEs). The non-substituted phenylene, hexylthiol-EDOT-phenyl-phosphonic acid, PA1, was synthesized and characterized as a means of model validity. PA1 absorbs in the UV region in its neutral state and upon oxidation absorbs within the visible, hence showcasing its potential as an ACE chromophore. The properties of PA1 inspired the designs of the other nine structural derivatives where the number and position of methoxy groups on the phenylene were varied. Using our DFT treatment, we assessed the impact of these modifications on the electronic structures, geometries, and excited-state properties. In particular, we examined stabilization intermolecular interactions (S-O and O-H) as they aid in molecule planarization, thus facilitating charge transport properties in devices. Additionally, destabilizing O-O forces were observed, thereby making some chromophores less desirable. A detailed excited state analysis was performed, which linked the simulated UV-Vis spectra to the dominant excited state transitions and their corresponding molecular orbitals. Based on these results, the nine chromophores were ranked ergo providing an ordered list of synthetic targets.

A full configuration interaction calculation (FCI) ultimately defines the innate molecular orbital description of a molecule. Its density matrix and the natural orbitals obtained from it quantify the difference between having N-dominantly occupied orbitals in a reference determinant for a wavefunction to describe N-correlated electrons and how many of those N-electrons are left to the remaining virtual orbitals. The latter provides a measure of the multi-determinantal character (MDC) required to be in a wavefunction. MDC is further split into a weak correlation part and a part that indicates stronger correlation often called multi-reference character (MRC). If several virtual orbitals have high occupation numbers, then one might argue that these additional orbitals should be allowed to have a larger role in the calculation, as in MR methods, such as MCSCF, MR-CI, or MR-coupled-cluster (MR-CC), to provide adequate approximations toward the FCI. However, there are problems with any of these MR methods that complicate the calculations compared to the uniformity and ease of application of single-reference CC calculations (SR-CC) and their operationally single-reference equation-of-motion (EOM-CC) extensions. As SR-CC theory is used in most of today's "predictive" calculations, an assessment of the accuracy of SR-CC at some truncation of the cluster operator would help to quantify how large an issue MRC actually is in a calculation, and how it might be alleviated while retaining the convenient SR computational character of CC/EOM-CC. This paper defines indices that identify MRC situations and help assess how reliable a given calculation is.

We studied the positron (e+) interaction with the hydrogen molecular dianion H22− to form the positronic bound state of [H−; e+; H−] using the first-principles quantum Monte Carlo method combined with the multi-component molecular orbital one. H22− itself is unstable, but it was shown that such an unbound H22− may become stable by intermediating a positron and forming the positronic covalent bond of the [H−; e+; H−] system [J. Charry et al., Angew. Chem., Int. Ed. 57, 8859–8864 (2018)]. We newly found that [H−; e+; H−] has double minima containing another positronic bound state of [H2; Ps−]-like configuration with the positronium negative ion Ps− at the bond distance approximately equal to the equilibrium H2 molecule. Our multi-component variational Monte Carlo calculation and the multi-component configuration interaction one resulted in the positronic covalent bonded structure being the global minimum, whereas a more sophisticated multi-component diffusion Monte Carlo calculation clearly showed that the [H2; Ps−]-like structure at the short bond distance is energetically more stable than the positronic covalent bonded one. The relaxation due to interparticle correlation effects pertinent to Ps− (or Ps) formation is crucial for the formation of the Ps−A2-like structure for binding a positron to the non-polar negatively charged dihydrogen.

The stable conformations of a series of bioactive molecules, (−)-alboatisins A–C, are identified via Monte Carlo searching with the MMFF94 molecular mechanics force field. Then, the optical rotation (OR) values, vibrational circular dichroism (VCD), and electronic circular dichroism (ECD) spectra were calculated using the gradient-corrected density functional theory method. The vibrational and transition modes of molecular chirality were explored in terms of their microscopic origin. The calculated specific rotations are in agreement with the experimental values. From the OR analysis, it was concluded that optical rotation values are regulated by hydroxyl substitution. Vibrations occurring on the chiral skeleton may cause strong absorption in VCD spectra; VCD spectra are thus the spectral response to deformation vibrations on the chiral carbon skeleton. The lowest-energy negative Cotton effect is caused by σ → π* transition. Frontier molecular orbital analysis showed that strong ECD absorptions are produc...

The mono and dihydrated complexes of 2′-deoxyguanosine have been used to elucidate the importance of the 2′-hydroxy group in the hydration. Density functional theory and time-dependent density functional theory methods were performed to investigate the ground-and excited-state hydrogen bonding properties of 2′-deoxyguanosine-water (2′-dG-W) and 2′-deoxyguanosine-2water (2′-dG-2W). Infrared spectra, geometric optimizations, frontier molecular orbitals and Mulliken charges have also been studied. The results demonstrated that the excited-state intramolecular hydrogen bonding dynamics of complexes 2′-dG-W and 2′-dG-2W behaves differently upon photoexcitation, while their intermolecular hydrogen bonding dynamics behaves similarly. Moreover, the significant weakening of the intermolecular hydrogen bond O4⋯H1–N1 and the formation of the new strong hydrogen bond O4⋯H3–N2 in the 2′-dG-2W upon photoexcitation were due to the geometric structure bending of guanine and the rigidity of related molecules. In addition,...

Directing energy and charge transfer processes in light-harvesting antenna systems is quintessential for optimizing the efficiency of molecular devices for artificial photosynthesis. In this work, we report a novel synthetic method to construct two regioisomeric antenna molecules (1-D2A2 and 7-D2A2), in which the 4-(n-butylamino)naphthalene monoimide energy and electron donor is attached to the perylene monoimide diester (PMIDE) acceptor at the 1- and 7-bay positions, respectively. The non-symmetric structure of PMIDE renders a polarized distribution of the frontier molecular orbitals along the long axis of this acceptor moiety, which differentiates the electron coupling between the donor, attached at either the 1- or the 7-position, and the acceptor. We demonstrate that directional control of the photo-driven charge transfer process has been obtained by engineering the molecular structure of the light-harvesting antenna molecules.

The characterization of an ionic liquid's properties based on structural information is a longstanding goal of computational chemistry, which has received much focus from ab initio and molecular dynamics calculations. This work examines kernel ridge regression models built from an experimental dataset of 2212 ionic liquid melting points consisting of diverse ion types. Structural descriptors, which have been shown to predict quantum mechanical properties of small neutral molecules within chemical accuracy, benefit from the addition of first-principles data related to the target property (molecular orbital energy, charge density profile, and interaction energy based on the geometry of a single ion pair) when predicting the melting point of ionic liquids. Out of the two chosen structural descriptors, ECFP4 circular fingerprints and the Coulomb matrix, the addition of molecular orbital energies and all quantum mechanical data to each descriptor, respectively, increases the accuracy of surrogate models for melting point prediction compared to using the structural descriptors alone. The best model, based on ECFP4 and molecular orbital energies, predicts ionic liquid melting points with an average mean absolute error of 29 K and, unlike group contribution methods, which have achieved similar results, is applicable to any type of ionic liquid.

We develop a full-quantum formulation of constrained nuclear-electronic orbital density functional theory (cNEO-DFT). This formulation deviates from the conventional Born-Oppenheimer framework, and all nuclei and electrons are treated on an equal footing within the molecular orbital picture. Compared to the conventional DFT, the ground state energy in full-quantum cNEO-DFT inherently includes all vibrational zero-point energies. We also derived and implemented the analytic gradient of the full-quantum cNEO-DFT energy with respect to the quantum nuclear expectation positions. With the analytic gradient, the geometry optimizations are performed, which naturally include the nuclear quantum effects and describe the geometric isotope effects. The full-quantum cNEO-DFT is tested on a series of small molecules and the transition states of two hydrogen transfer reactions. The results are compared with those from conventional DFT, DFT-VPT2, and NEO-DFT with only key protons treated quantum mechanically. It is found that the nuclear quantum effects have notable impacts on molecular equilibrium geometries and transition state geometries. The full-quantum cNEO-DFT can be a promising method for describing the nuclear quantum effects in many chemical processes.

The threshold photoelectron spectrum (TPES) of halocyclohexanes C6H11X (X = Cl, Br, and I) was recorded at the Swiss Light Source and assigned with the help of density functional theory and equation-of-motion ionization potential coupled cluster calculations. Dyson orbitals show that the first two electronic states of the cation arise by symmetry breaking of the doubly degenerate eg orbitals in cyclohexane as perturbed by the halogen or by perturbation of the halogen lone pair by the cyclohexane ring scaffold in the case of light and heavy halogen substituents, respectively. When the resulting two states (A″ and A') are coupled via a conical intersection in CS symmetry, they are smoothly connected by molecular orbital rotation when the nuclear symmetry is relaxed. Even then, barriers at avoided crossings lead to distinct A' and pseudo-A″ minima, which contribute to the TPES separately. As axial and equatorial conformers are present in commensurate abundance at room temperature, four transitions are conceivable for each substituent in the low-energy range. Three of these could be identified, and their energy could be determined for each sample. Transitions to A' states are associated with a smaller geometry change and exhibit stronger origin transitions. Yet, most notably in X = Br, they do not correspond to the adiabatic ionization energy, which is indicated by a weak and broad band to the pseudo-A″ state with a lower onset energy. Franck-Condon vibrational analysis of the TPES coupled with quantum chemical calculations can provide insights into the behavior of conformers as well as strongly coupled electronic states.

In recently developed non-fullerene acceptor (NFA) based organic solar cells (OSCs), both the donor and acceptor parts can be excited by absorbing light photons. Therefore, both the electron transfer and hole transfer channels could occur at the donor/acceptor interface for generating free charge carriers in NFA based OSCs. However, in many molecular and DNA systems, recent studies revealed that the high charge transfer (CT) efficiency cannot be reasonably explained by a CT model with only highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of donor and acceptor molecules. In this work, taking an example of a full-polymer blend consisting of benzodithiophene-alt-benzotriazole copolymers (J51) as donor and naphthalene diimide-bithiophene (N2200) as acceptor, in which the ultrafast hole transfer has been recently reported, we investigate its CT process and examine the different roles of various frontier molecular orbitals (FMOs). Through a joint study of quantum mechanics electronic structure calculation and nonadiabatic dynamics simulation, we find that the hole transfer between HOMOs of J51 and N2200 can hardly happen, but the hole transfer from HOMO of N2200 to HOMO - 1 of J51 is much more efficient. This points out the underlying importance of the deep hole channel in the CT process and indicates that including FMOs other than HOMOs and LUMOs is highly necessary to build a robust physical model for studying the CT process in molecular optoelectronic materials.

Boron can form strong bonds with transition metals in diatomic metal borides (MB), but the nature of the chemical bonding has not been well understood. Recently, a quadruple bond was discovered in Rh≣B, consisting of two σ bonds formed between the Rh 4dz2 and B 2s/2p orbitals and two π bonds between the Rh 4dxz/4dyz and the B 2px/2py orbitals. The bonding between the 5d transition metals and boron is expected to be even stronger. Here, we report an investigation on the electronic structure and chemical bonding of the 5d transition metal diatomic borides (IrB, PtB, and AuB) using high-resolution photoelectron imaging on the corresponding anions (MB-) and theoretical calculations. Vibrationally resolved photoelectron spectra are obtained for all three anions, and the electron affinities are measured for IrB, PtB, and AuB to be 1.995(1), 2.153(3), and 0.877(6) eV, respectively. It is found that the weakly anti-bonding 3σ molecular orbital (mainly of M 6s and B sp characters) is singly occupied in IrB (3Δ) and PtB (2Σ+), resulting in a bond order of three and half for these two diatomic borides. The 3σ orbital is doubly occupied in AuB (1Σ+), giving rise to a weak triple bond. Despite the lower bond order, the bonding in IrB and PtB is only slightly weaker than that in RhB due to the more favorable interactions between the M 5d orbitals and the B sp orbitals.

The strong inter-relationship between cyclohepta-1,3,5-triene (CHT) and norcaradiene (NCD) systems observed in some reactions has been extended to include the energy surfaces for some low-lying ionic states. Equilibrium structures for ionic states of CHT with 2A′ symmetry were routinely found; the structures emerging with 2A′′ symmetry were NCD ionic states. A detailed analysis of these surfaces as a function of the C1 to C6 distance showed that while minima occurred for both state symmetries, curve crossing occurs in CS symmetry, which is avoided by distortion to C1 symmetry. The CHT → NCD structural change is attributed to initial conrotatory closure of the singly occupied molecular orbital. A new synchrotron-based photoelectron spectrum (PES) for CHT up to 25 eV shows little vibrational structure. We have assigned the PES up to 17 eV using a variety of theoretical methods. The calculated lowest ionic state, X2A′, is predicted to have a very low vibrational frequency of 87 cm−1, leading to a high density of vibrational states. The Franck–Condon envelopes calculated for the two lowest states are almost completely contained within the envelope of the lowest PES band. A comparison of the predicted PES of CHT and NCD showed much closer agreement of the PES with that of CHT. An analysis of the 1H and 13C nuclear magnetic resonance (NMR) spectra of CHT showed no evidence of NCD. The increased chemical shifts arising from the higher frequencies used here lead to significant changes in appearance when compared with earlier NMR spectra.

Ionizing interactions between charged particles and molecules of biological relevance have attracted considerable interest in the last decade due to its importance in medical radiation therapy. We have previously calculated triply differential cross sections for five biomolecules in collaboration with experimental groups. We used the molecular 3-body distorted wave approximation for these calculations. For ionization of biomolecules, experimentalists are unable to determine the orientation of the molecule at the time of ionization, which means that the calculated cross sections need to be averaged over all molecular orientations. At the time the calculations were performed, it was not numerically feasible for us to perform proper averaging over orientations, so we introduced the orientation averaged molecular orbital approximation to make the calculations possible. We now have the computational capability to properly perform this average, so, here, we present new results with a proper average over orientations and compare with the previous calculations and experiment. Since the original calculations, results from two different distorted-wave models have also been published and the new results will also be compared with those calculations. Overall, the new results are in better agreement with the experiment.

C6F12O can be used in gas-insulated equipment due to its excellent insulation properties. The purpose of this paper is to calculate the total electron-impact ionization cross section to evaluate the dielectric strength of the molecule using the Deutsch–Märk formula. First, according to the calculation method of quantum chemistry, the structure of the molecule is optimized. Three different methods, such as Mulliken population analysis, C-squared population analysis, and natural atomic orbital (NAO), are used to calculate the molecular orbital components, and then the molecular collision cross section is obtained. The influence of different weighting factors on the calculation results is analyzed. The validity of the proposed method is verified by the calculation results of H2O, C3H6O, and C5F10O. The results show that the calculation value with the NAO method is closer to the experimental results, which provides a reference for the calculation and analysis of the collision cross section of C6F12O. The calculation results in this paper can provide basic data for further calculation of the dielectric strength of C6F12O.

Apart from being a unique material for efficient solar cells, hybrid halide perovskites possess more mysteries than ever. An anomalous bandgap behavior in CH3NH3Sn1−xPbxI3 alloys has been reported recently [Hao et al., J. Am. Chem. Soc. 136, 8094 (2014)], in which the composition-dependent optical bandgap follows nonmonotonic and nonlinear characteristics instead of a linear trend or Vegard's law; the bandgap of the intermediate compounds was lower than that of the end members. In this article, we study composition-dependent conduction and valence band energies through scanning tunneling spectroscopy to deliberate on the role of the two bands in the bandgap bowing phenomenon and the underlying mechanism. We observe a nonlinear behavior of the two bands with respect to the alloy composition, leading to an anomalous behavior in the transport gap as well. We confirm that two competing events, namely, a spin–orbit coupling parameter appearing due to inclusion of a high-Z material and structural distortion affecting molecular orbitals responsible for the formation of the valence and the conduction bands, result in bandgap bowing in CH3NH3Sn1−xPbxI3 alloys.

Occupied and unoccupied electronic structures of submonolayer perylene (C20H12) on a graphite surface have been investigated using two-photon photoemission (2PPE) spectroscopy for two phases at room and low temperatures. Low energy electron diffraction measurements indicated that the molecules are disordered at room temperature and form a well-ordered superstructure below 180 K. In 2PPE, a specific unoccupied peak (Lx) was observed at around room temperature (>180 K) but not at low temperature (

Two-dimensional electron density map (2D map) of binding energy and relative azimuthal angle (i.e., momentum) for the outer-valence molecular orbitals of SF6 has been measured by a highly sensitive electron momentum spectrometer with noncoplanar symmetric geometry at the impact energy of 1.2 keV plus binding energy. The experimental electron momentum profiles for the relevant molecular orbitals have been extracted from the 2D map and interpreted on the basis of the quantitative calculations using the density functional theory with B3LYP hybrid functional. For the outermost F2p nonbonding orbitals of SF6, the interference patterns are clearly observed in the ratios of the electron momentum profiles of molecular orbitals to that of atomic F2p orbital.

Analogous to atoms, superatoms can be used as building blocks to compose molecules and materials. To demonstrate this idea, the possibility of using tetrahedral Ag4 cluster to form a series of superatomic molecules Ag4X4 (X=H, Li, Na, K, Cu, Ag, Au and F, Cl, Br) is discussed. Based on the super valence bond model, a tetrahedral Ag4 cluster can be viewed as a 4-electron superatom, which can mimic a sp3 hybridization C atom. By comparison of the representative superatomic molecules Ag4X4 (X=Au, Cl) with the corresponding simple molecules CX4 (X=H, Cl), the similarities in terms of chemical bonding patterns and molecular orbitals (MOs) are conspicuous. Energy calculations predict that the Ag4 superatom can bind with all the involved ligands. Furthermore, the stabilities of superatomic molecules are enhanced by the large gaps of the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO gaps) and high aromaticity. Our studies may find applications in assembling materials with superatoms.