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Papers by Vladimir Tsirelson

Mendeleev Communications, 2020

The results of quantum mechanics/molecular mechanics calculations of electron density changes upo... more The results of quantum mechanics/molecular mechanics calculations of electron density changes upon oligopeptide hydrolysis by the matrix metalloproteinase-2 are utilized to discriminate between reactive and non-reactive enzyme–substrate complexes. Electron density depletion regions on the carbonyl carbon atom attacked by a catalytic water molecule are found on the 2D maps of electron density Laplacian in the reactive complexes. Also, the computed Fukui function quantitatively describes reactivity of the nucleophilic and electrophilic sites.

$Research paper thumbnail of Diffraction Methods for the Investigation of the Electron Density and Dynamics of Crystal Lattices$

Russian Chemical Reviews, 1986

The d.c. Hall coefficient and resistivity of six semiconducting diamonds have been measured as a ... more The d.c. Hall coefficient and resistivity of six semiconducting diamonds have been measured as a function of temperature from 200 to 800"~. All the diamonds were p-type semiconductors. From the measurements the effective mass of the charge carriers, the concentration of donor and acceptor centres, the activation energy of the acceptors (close to 0.34 ev) and the temperature dependence of the Hall mobility have been calculated. At high temperatures the mobility varies as T-2'a. The relative strengths of certain peaks in the infra-red absorption spectrum are the same in different specimens. It is concluded that all these peaks are due to the Same centre. These peaks are not detected in type I and type IIa diamonds. There is a strong correlation between the strength of the strongest peak at 0.346 ev and the number of vacant acceptor levels at room temperature, from which it is concluded that the centre giving rise to the peaks is also responsible for conduction.

Materials Research Bulletin, 1996

PREFACE INTRODUCTION: THE ELECTRON DENSITY CONCEPT IN PHYSICS AND CHEMISTRY THEORY Computational ... more PREFACE INTRODUCTION: THE ELECTRON DENSITY CONCEPT IN PHYSICS AND CHEMISTRY THEORY Computational ground state quantum chemistry Methods of the density functional theory Quality of the theoretical electron densities Quantum mechanics and topology of the electron density Electric field characteristics of molecules and crystals X-RAY DIFFRACTION EXPERIMENT Physical principles of the electron density reconstruction Precise measurements of the diffracted x-ray beam intensities From intensities to kinematic structure amplitudes Crystallographic structural models Quantum-chemical models Electron densities via Fourier series Accuracy of the experimental electron density NEW AND COMPLIMENTARY METHODS IN THE ELECTRON DENSITY STUDY Synchrotron radiation in the x-ray diffractometry Gamma-diffractometry Precise structure amplitude determination by Pendellosung effect High energy electron diffraction Schwinger scattering of neutrons MAGNETIZATION AND SPIN DENSITY ELECTRON DENSITY AND THE CHEMICAL BOND Concepts of the electron density analysis Atomic charges and pseudoatomic moments Deformation electron density Quantum topological theory of the chemical bond Nature of the chemical bond ELECTRON DENSITY AND CRYSTAL PROPERTIES Electrostatic effects Diamagnetic susceptibility Optical characteristics Concluding remarks APPENDICES Systems of units Vibrating atoms in crystals as quantum oscillators Atomic orbitals and their analytical approximations Electrostatic potential distribution in atoms Creation and annihilation operators Reciprocal space Thermal diffuse scattering of x-rays and neutrons Statistics in the x-ray structure analysis Fourier transformations of atomic orbital products Least squares in crystallographic structural models refinement Neutrons in electron density studies REFERENCES INDEX

$Research paper thumbnail of Precision x-ray diffraction study of the garnets Na3Sc2V3O12 and Na0.90Ca2.38Mn1.72V3O12$

Journal of Structural Chemistry, 1989

The distribution of electron density and electrostatic potential in the compounds Na3Sc2V3Oz2 (Sc... more The distribution of electron density and electrostatic potential in the compounds Na3Sc2V3Oz2 (ScVG) and Na0.s0Ca2.ssMnz.72V3Oz2 (MnVG) with garnet structure was studied by precision x-ray diffraction. Refinement of the structure using reflections chosen by a special method from the outer region of reciprocal space led to R = 0.0085, R w = 0.0071, S = 1.006 (ScVG) and R = 0.0058, Rw = 0.0049, S = 1.079 (MnVG). Maps of deformed electron density and deformed electrostatic potential were constructed and their interpretation given in terms of MO. Features of the electronic structure in the crystals studied have a confidence level not lower than 95%.

The Journal of Chemical Physics, 1968

The electric field gradient at either nucleus in H2+ is calculated from electronic wavefunctions ... more The electric field gradient at either nucleus in H2+ is calculated from electronic wavefunctions which use two kinds of basis sets. One basis set is composed entirely of Gaussian-type functions and the other, the so-called improved set, includes an additional function of the form, χ = (ρ − r)l for r ≤ ρ, χ = 0 for r > ρ, centered on each nucleus, where r is the distance from the nucleus and ρ and l are parameters chosen to minimize the electronic energy. The purpose of this χ function is to improve the quality of the wavefunction near the nuclei. The effect of such a function on the electric field gradient at a nucleus is determined in this paper.

Accounts of Chemical Research, 2006

$Research paper thumbnail of Electron density and electrostatic potential of KNiF<sub>3</sub>: multipole, orbital and topological analyses of vacuum-camera-imaging plate and four-circle diffractometer data$

Acta crystallographica, Dec 1, 1999

The electron density and electrostatic potential of KNiF 3 crystal were studied using multipole a... more The electron density and electrostatic potential of KNiF 3 crystal were studied using multipole and orbital model treatment of the precision X-ray diffraction data measured by vacuum camera imaging plate and by fourcircle diffractometer methods. Different experimental methods lead to close multipole and atomic displacement parameters and to the qualitatively same electron densities. Good agreement was also achieved for the Laplacians of the electron density and the electrostatic potentials. Some pitfalls of the vacuum camera imaging plate method that could be improved are discussed. * minimal extinction correction, # c is a coefficient in the expression for a weighting scheme: w=1/[σ σ σ σ 2 (|F|)+c |F| 2 ].

Crystals

In order to understand the phenomenon of negative linear compressibility (NLC) in organic crystal... more In order to understand the phenomenon of negative linear compressibility (NLC) in organic crystals, it is necessary to investigate not only the structural features but also the electronic changes taking place under external hydrostatic pressure. It is also necessary to clarify which electronic properties allow the quantification and comparison of the compressibility of crystals. In our study, the crystal structures of sodium and cadmium formates under hydrostatic compression were modeled, as well as the α and β-phases of calcium formate. The changes in cell parameters and spatial dependences of the linear compressibility were analyzed, and the ranges of external pressure, which must be applied for NLC onset, were predicted for the sodium and α-calcium formates. Although the behavior of chemical bonds is not predicted by the sign or absolute value of the quantum electronic pressure, its relative change under external pressure clearly distinguishes the soft and rigid regions in a crys...

Crystal Growth & Design

$Research paper thumbnail of Precision X-ray diffraction study of KTaO 3 :Li crystals$

Crystallography Reports, Sep 1, 1995

$Research paper thumbnail of Determination of the coefficients of the representation of the one-electron density matrix of a crystal from x-ray diffraction data$

Soviet physics. Doklady, Aug 1, 1983

Proceedings of the USSR Academy of Sciences, 1989

Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials, 2020

Quantum theory of atoms in molecules and the orbital-free density functional theory (DFT) are com... more Quantum theory of atoms in molecules and the orbital-free density functional theory (DFT) are combined in this work to study the spatial distribution of electrostatic and quantum electronic forces acting in stable crystals. The electron distribution is determined by electrostatic electron mutual repulsion corrected for exchange and correlation, their attraction to nuclei and by electron kinetic energy. The latter defines the spread of permissible variations in the electron momentum resulting from the de Broglie relationship and uncertainty principle, as far as the limitations of Pauli principle and the presence of atomic nuclei and other electrons allow. All forces are expressed via kinetic and DFT potentials and then defined in terms of the experimental electron density and its derivatives; hence, this approach may be considered as orbital-free quantum crystallography. The net force acting on an electron in a crystal at equilibrium is zero everywhere, presenting a balance of the ki...