Quantum-chemical methods of studying the electronic structure of molecules and diffraction experiments

Energy Density Functional Theory of Many-Electron Systems

“…We postulate that for a given molecular system in a certain state with a one-electron density p(T), there exists a definite "promolecular" state, or a "promolecule", characterized by the N-electron wavefunction 1>prom E £N with an associated pprom(i) (Hirschfeld and Rzotkiewicz, 1974;Avery, 1979;Avery and Ormen, 1980;Avery and Berg, 1979;Coppens, 1977;Tsirelson and Ozerov, 1978;Tsirelson, 1986; see also Section 3.4) We postulate that for a given molecular system in a certain state with a one-electron density p(T), there exists a definite "promolecular" state, or a "promolecule", characterized by the N-electron wavefunction 1>prom E £N with an associated pprom(i) (Hirschfeld and Rzotkiewicz, 1974;Avery, 1979;Avery and Ormen, 1980;Avery and Berg, 1979;Coppens, 1977;Tsirelson and Ozerov, 1978;Tsirelson, 1986; see also Section 3.4)…”

The Relationship between the Antimicrobial Properties of Benzylpenicillin and the Quantum Chemical Parameters of Its Structure (The DFT Method)

“…To examine the relationship between the antimicrobial properties of penicillin and its electronic structure the quantum chemical DFT-PBE0 / 6-311G ** method was chosen (Perdew-Burke-Ernzerhof 1996 nonlocal, Perdew-Wang 1991 LDA) [7]. It is known that the DFT method (Nobel Prize W. Kohn, 1998), based on the theory of density of functionality, can significantly improve the accuracy of the calculation of the energy of the complex molecular systems to which benzylpenicillin refers [8]. Besides, it makes a good description of the distribution of the electron density in the ground state.…”

X-ray Charge Density Study of the Drug Methimazole with Z′ = 2: Differences in the Electronic Structure of the Thiourea Core due to Crystal Packing Effects

“…To this end, the Quantum Theory of Atoms in Molecules developed by Bader , greatly complements the general charge density techniques. In particular, many recent works have dealt with the qualitative and quantitative description of chemical bonding, , especially individual studies focusing on various structural properties of widely known active pharmaceutical ingredients − that had greatly contributed to medicinal chemistry.…”

“…In all of these polymorphs, the compound is present in the thione tautomeric form. The main crystalforming motif in all methimazole phases is the hydrogenbonded dimer with a graph descriptor R 2 2 (8). Interestingly, for the α phases, this dimer is somewhat bent, meaning that two molecules do not lie on a single plane.…”