Polarization energies,transport gap and charge transfer states of organic molecular crystals

A self-consistent calculation of electronic polarization in organic molecular crystals and thin films is presented in terms of charge redistribution in nonoverlapping molecules in a lattice. The polarization energies P₊ and P₋ of a molecular cation and anion are found for anthracene and perelynetetracarboxylic dianhydride (PTCDA), together with binding energies of ion pairs and transport gaps of PTCDA films on metallic substrates. The 500 meV variation of P₊+P₋ with film thickness agrees with experiment, as do calculated dielectric tensors. Comparisons are made to submolecular calculations in crystals.     

Method of calculating band shape for molecular electronic spectra

A method for approximating the band shape of molecular electronic transitions based on a single geometric configuration is described. The band shape is modeled using an empirical parameter to estimate the width at half-height for each transition. In addition to generating a shape for allowed transitions, a procedure is developed for approximating the oscillator strength for the symmetry forbidden bands. The results obtained using these two approximations are then compared with experimental spectra and to the results obtained from stochastic methods for simple organic molecules, such as benzene, naphthalene, and the diazobenzenes. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 781–796, 1998     

Concerning virial-based estimations of strength of bonding intermolecular interactions in molecular crystals and supramolecular complexes

It is shown that the electronic virial-based correlation should be used to estimate bonding contributions to the rigidity of molecular vibrations in crystals.     

Investigation of molecule properties from electronic absorption spectra of solid and liquid crystals

Among the achievements of 20th century, there is the origin and violent development of the low-temperature technique and low-temperature spectroscopy of molecular crystals in the polarized light. Many obtained results became possible due to the close cooperation between experiment investigators and theorists. This short review traces the evolution of only one trend in the physics of molecular crystals, namely, the investigation of energetic and spatial structure of molecules from the analysis of electronic spectra of molecular crystals. First, for this purpose the possibilities of using the electronic spectra of molecular crystals at low temperatures benzene derivatives and the electronic spectra of liquid ionic crystals are considered. The results of investigations of the electronic absorption spectra for the new class of liquid crystals, namely, ionic metal-organic smectics are presented. Changes in the structure of doping molecules in the ionic liquid crystals under the influence of the dc electric field are analyzed.     

Comments on group theoretical analysis of NQR spectra of crystals

The use of generating function methods for the number of NQR lines of crystals exhibiting distortion is outlined. The intensity ratios of NQR lines can be obtained using a double coset method.     

Computationally-assisted approach to the vibrational spectra of molecular crystals: study of hydrogen-bonding and pseudo-polymorphism.

A new computationally-assisted methodology (PiMM), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suitable molecular pairs, using the B3LYP/6-31G* approach.The proposed methodology provides an answer to the current demand for a reliable assignment of the vibrational spectra of these methyl-xanthines, and clarifies several misleading assignments. The most relevant intermolecular interactions in each system and their effect on the vibrational spectra are considered and discussed. Based on these results, significant insights are obtained for the structure of caffeine in the anhydrous form (stable at room temperature), for which no X-ray structure has been reported. A possible structure based on C((8))--H...N((9)) and C((1,3))--H...O intermolecular interactions is suggested.     

Methods for calculating the enthalpies of sublimation of organic molecular crystals

Four methods for calculating the enthalpies of sublimation of organic molecular crystals based on different methodological approaches are proposed. Comparative analysis of these methods was carried out and their good predictive ability with respect to various classes of compounds (aliphatic nitro compounds, acyclic and cyclic amines, amides and amino acids, benzene derivatives, heterocyclic compounds,etc.) was demonstrated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No, 12, pp. 2872–2881, December, 1996.     

Non-empirical molecular orbital theory of the electronic structure of molecular crystals

A non-empirical molecular orbital treatment of molecular crystals, based on SCF perturbation theory and matrix partitioning methods is presented.     

Electronic energy structure of MBiS2 (M = Li, Na, K) calculated with allowance for the difference between the M-S and Bi-S bond lengths

The modified augmented plane wave method (WIEN2k program) was used to study the electronic energy structure and calculate the SK-absorption spectra of LiBiS₂, NaBiS₂, and KBiS₂. The crystal structures of the compounds were modeled using symmetric structures, in which each sulfur atom was surrounded by three alkali metal atoms and three bismuth atoms in such a way that the alkali metal-sulfur and bismuth-sulfur bond length differed. This difference between bond lengths was calculated from the sum of the ionic radii of the components of compounds and by the geometry optimization of the crystal lattice. The two variants of calculation allowed us to check the applicability of Pauling’s idea about preservation of the bond lengths of elements in compounds for modeling the crystal structures of LiBiS₂, NaBiS₂, and KBiS₂. The SK absorption spectra and optically forbidden bands were calculated.     

A new energy decomposition scheme for molecular interactions within the Hartree-Fock approximation

A new method is proposed for the analysis of components of molecular interaction energy within the Hartree-Fock approximation. The Hartree-Fock molecular orbitals of the isolated molecules are used as the basis for the construction of Fock matrix of the supermolecule. Then certain blocks of this matrix are set to zero subject to specify boundary conditions of the supermolecule molecular orbitals, and the resultant matrix is diagonalized iteratively to obtain the desired energy components. This method can be considered as an extension of our previous method, but has an advantage in the explicit definition of the charge transfer energy, placing it on an equal footing with the exchange and polarization terms. The new method is compared with existing perturbation methods, and is also applied to the energy and electron density decomposition of (H₂O)₂.     

To the question on radiationless transitions in electronically excited zones of molecular crystals

A model is proposed describing the dynamics of radiationless transitions in the energy zones corresponding to excited electronic states in molecular crystals. In this model, the migration effect is explicitly reflected, which initially appears under pulse excitation of the systems with a periodical structure of a density distribution of states in separate parts of molecular crystals.     

Influence of molecular electronic properties on the IR spectra of dimeric hydrogen bond systems: polarized spectra of 2-hydroxybenzothiazole and 2-mercaptobenzothiazole crystals

We have studied the polarized IR spectra of the hydrogen-bonded molecular crystals of 2-hydroxybenzothiazole (HBT) and 2-mercaptobenzothiazole (MBT). The crystal structure of 2-hydroxybenzothiazole was determined by X-ray diffraction. The polarized spectra of the crystals were measured, in the frequency ranges of the ν_N-H and ν_N-D bands, at room temperature, and at 77 K. In both systems an extremely strong H/D isotopic effect in the spectra was observed, involving reduction of the well-developed ν_N-H band fine structure to a single prominent ν_N-D line only. The two ν_N-H bands were also shown to exhibit almost identical properties, band shapes, temperature and dichroic properties included. The spectra were quantitatively reconstituted, along with the strong isotopic effect, when calculated using the ‘strong-coupling’ theory, assuming the centrosymmetric dimers of HBT or MBT to be the structural units responsible for the crystalline spectral properties. The similarity of the spectra of the two crystalline systems was considered to be a result of longer-distance couplings between the proton vibrations in the dimers, via the aromatic ring electrons. When investigating the ‘residual’ ν_N-H band shapes for crystals isotopically diluted by deuterium, we observed some ‘self-organization’ effects in the spectra, indicating the energetically favored presence of two identical hydrogen isotopes in each hydrogen bond dimer.     

A highly efficient hybrid method for calculating the hydration free energy of a protein

We develop a new method for calculating the hydration free energy (HFE) of a protein with any net charge. The polar part of the energetic component in the HFE is expressed as a linear combination of four geometric measures (GMs) of the protein structure and the generalized Born (GB) energy plus a constant. The other constituents in the HFE are expressed as linear combinations of the four GMs. The coefficients (including the constant) in the linear combinations are determined using the three‐dimensional reference interaction site model (3D‐RISM) theory applied to sufficiently many protein structures. Once the coefficients are determined, the HFE and its constituents of any other protein structure are obtained simply by calculating the four GMs and GB energy. Our method and the 3D‐RISM theory give perfectly correlated results. Nevertheless, the computation time required in our method is over four orders of magnitude shorter.     

A simple model for the calculation of HOMO and LUMO energy levels of benzocatafusenes

A simple model for the calculation of HOMO and LUMO energy levels of benzocatafusenes (i.e., molecules that are only constituted by mutually condensed benzene rings and without interior carbon atoms, which belong to three benzene rings) is presented. Using semiempirical AM1 method, 615 benzocatafusenes were studied (29 normal and 586 branched). The relation between energy and molecular structure was coded by the three Hückel parameters: Coulomb integral, bond integral, and secular x eigenvalue. Analytical functions for HOMO and LUMO energy levels in terms of x parameter were obtained for normal benzocatafusenes, and energies for branched benzocatafusenes were satisfactorily modelled by the introduction of a simple correction function into the analytical functions describing normal benzocatafusenes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Anisotropy analysis of the surface energy of diamond cubic crystals

The surface energies for 24 surfaces of diamond structure cubic crystals of C, Si and Ge have been calculated using the modified embedded‐atom method. The results show that the three lowest surface energies correspond to the (111), (211) and (433) surfaces. Considering surface energy minimization solely, the (111), (211) and (433) textures should be favourable successively in diamond cubic films. The appearance of abnormal grains or textures with (111) and (211) orientations in Si, Ge and C films results from surface energy minimization. Copyright © 2003 John Wiley & Sons, Ltd.