Papers by Boris Tsukerblat

Magnetochemistry
We discuss the problem of electron transfer (ET) in mixed valence (MV) molecules that is at the c... more We discuss the problem of electron transfer (ET) in mixed valence (MV) molecules that is at the core of molecular Quantum Cellular Automata (QCA) functioning. Theoretical modelling of tetrameric bi-electronic MV molecular square (prototype of basic QCA cell) is reported. The model involves interelectronic Coulomb repulsion, vibronic coupling and ET between the neighboring redox sites. Unlike the majority of previous studies in which molecular QCA have been analyzed only for particular case when the Coulomb repulsion energy significantly exceeds the ET energy, here we do not imply assumptions on the relative strength of these two interactions. Moreover, in the present work we go beyond the adiabatic semiclassical approximation often used in theoretical analysis of such systems in spite of the fact that this approximation ignores such an important phenomenon as quantum tunneling. By analyzing the electronic density distributions in the cells and the ell-cell response functions obtaine...

The Journal of Chemical Physics
Strong Coulomb repulsion between the two charges in a square planar mixed-valence cell in quantum... more Strong Coulomb repulsion between the two charges in a square planar mixed-valence cell in quantum cellular automata (QCA) allows us to encode the binary information in the two energetically beneficial diagonal distributions of the electronic density. In this article, we pose a question: to what extent is this condition obligatory for the design of the molecular cell? To answer this question, we examine the ability to use a square-planar cell composed of one-electron mixed valence dimers to function in QCA in a general case when the intracell Coulomb interaction U is not supposed to be extremely strong, which means that it is comparable with the characteristic electron transfer energy (violated strong U limit). Using the two-mode vibronic model treated within the semiclassical (adiabatic) and quantum-mechanical approaches, we demonstrate that strong vibronic coupling is able to create a considerable barrier between the two diagonal-type charge configurations, thus ensuring bistabilit...

Chemistry Journal of Moldova, 2007
In this paper we give a short overview of our efforts in the understanding of the magnetic proper... more In this paper we give a short overview of our efforts in the understanding of the magnetic properties of the fascinating nanoscopic cluster K6[VIV15As6O42(H2O)]·8H2O (hereafter V15) exhibiting layers of magnetization. We analyze EPR and adiabatic magnetization of the V15 cluster with a triangular VIV3 array causing spin frustration. A model for V15 includes isotropic and antisymmetric (AS) exchange interactions in the general form compatible with the trigonal symmetry. Orientation of the AS vector (but not only its absolute value) is shown to play an important physical role in spin-frustrated systems. We were able to reach perfect fit to the experimental data on the stepwise dependence of magnetization vs. field at ultra-low temperatures. Furthermore, it was possible for the first time to estimate precisely two components of the AS vector coupling constant, namely, in-plane component and the perpendicular part. We show that only intramultiplet transitions in EPR are allowed when the...

Magnetochemistry, 2021
In this article, we apply the two-mode vibronic model to the study of the dimeric molecular mixed... more In this article, we apply the two-mode vibronic model to the study of the dimeric molecular mixed-valence cell for quantum cellular automata. As such, we consider a multielectron mixed valence binuclear d2−d1–type cluster, in which the double exchange, as well as the Heisenberg-Dirac-Van Vleck exchange interactions are operative, and also the local (“breathing”) and intercenter vibrational modes are taken into account. The calculations of spin-vibronic energy spectra and the “cell-cell”-response function are carried out using quantum-mechanical two-mode vibronic approach based on the numerical solution of the dynamic vibronic problem. The obtained results demonstrate a possibility of combining the function of molecular QCA with that of spin switching in one electronic device and are expected to be useful from the point of view of the rational design of such multifunctional molecular electronic devices.

ChemPhysChem, 2021
The effects of the vibronic coupling in quantum cellular automata (QCA) based on the square plana... more The effects of the vibronic coupling in quantum cellular automata (QCA) based on the square planar mixed valence (MV) molecular cells comprising four paramagnetic centers (spin cores) and two excess mobile electrons are analyzed in the important particular case when the Coulomb energy gap between the ground antipodal diagonal‐type two‐electron configurations and the excited side‐type configurations considerably exceeds both the one‐electron transfer parameter (strong U‐limit) and the vibronic stabilization energy. Under such conditions the developed model involves the second‐order double exchange, the Heisenberg‐Dirac‐Van Vleck (HDVV) exchange and the vibronic coupling of the excess electrons with the molecular B1g‐vibration composed of four full‐symmetric local vibrations. The latter interaction is shown to significant amplify the ability of the electric field produced by the driver‐cell to polarize the excess electrons in the working cell, which can be termed “the effect of the vi...

Magnetochemistry, 2020
The effect of the double exchange in a square-planar mixed-valence dn+1−dn+1−dn−dn–type tetramers... more The effect of the double exchange in a square-planar mixed-valence dn+1−dn+1−dn−dn–type tetramers comprising two excess electrons delocalized over four spin cores is discussed. The detailed analysis of a relatively simple d2−d2−d1−d1–type tetramer shows that in system with the delocalized electronic pair the double exchange is able to produce antiferromagnetic spin alignment. This is drastically different from the customary ferromagnetic effect of the double exchange which is well established for mixed-valence dimers and tetramers with one excess electron or hole. That is why the question “Can double exchange cause antiferromagnetic spin alignment?” became the title of this article. As an answer to this question the qualitative and quantitative study revealed that due to antiparallel directions of spins of the two mobile electrons which give competitive contributions to the overall polarization of spin cores, the system entirely becomes antiferromagnetic. It has been also shown that...

International Reviews in Physical Chemistry, 2020
The purpose of this article is to answer the question of how symmetry helps us to investigate and... more The purpose of this article is to answer the question of how symmetry helps us to investigate and understand the properties of nanoscopic magnetic clusters with complex structures. The systems of choice will be the three types of polyoxometalates (POMs): (1) POMs containing localised spins; (2) reduced mixed-valence (MV) POMs; (3) partially delocalised POMs in which localised and delocalised subunits coexist and interact. The theoretical tools based on various kinds of symmetry are the following: (1) irreducible tensor operator (ITO) approach based on the so-called "spin-symmetry" and MAGPACK program; (2) group-theoretical assignment of the exchange multiplets based on spin-and point symmetries; (3) group-theoretical classification of the delocalised electronic and electron-vibrational states of MV POMs; (4) general approach (based on spin symmetry) to evaluate the energy levels of large MV clusters and the corresponding MVPACK program; (5) computational approach (employing point symmetry) to solve multidimensional non-adiabatic vibronic problems in the nanoscopic systems realized as VIBPACK software. We made it our goal to avoid a conventional deductive style of presentation. On the contrary, we first consider specially selected complex POMs and then show by what methods and in what way the theoretical problems arising in the description of the properties of these molecules can be properly solved.
Acta Physica Polonica A, 2018
In this article we summarize the study of the electronic states and electron-vibrational interact... more In this article we summarize the study of the electronic states and electron-vibrational interactions in squareplanar molecular entities playing the role of molecular cells in quantum cellular automata (QCA), a promising paradigm of quantum computing. The following issues are shortly discussed: 1) QCA as a paradigm of quantum computing; 2) molecular implementation of QCA; 3) vibronic coupling as the origin of charge trapping, encoding of binary information 4) non-linear cell-cell response; 4) spin-switching in molecular QCA based on mixed-valence cells; 5) multimode dynamic vibronic problem, the symmetry assisted approach.
The Journal of Physical Chemistry C, 2019
Here we propose a vibronic pseudo Jahn-Teller (JT) model for partially delocalized mixed valence ... more Here we propose a vibronic pseudo Jahn-Teller (JT) model for partially delocalized mixed valence (MV) molecules aimed to the description of the magnetic coupling between the localized spins mediated by the delocalized electron. The model involves the following key interactions: electron transfer in the spin-delocalized subsystem which is mimicked by a dimeric unit, coupling of the itinerant electrons with the molecular vibrations and isotropic magnetic exchange between the localized spins and delocalized electron. The pseudo JT vibronic coupling which is considered in the framework of the Piepho, Krausz and Schatz (PKS) model adapted to the case of partially delocalized MV molecules. It is revealed (qualitatively and quantitively) how the vibronic coupling affects the connection of the localized spins via the itinerant electron.

Pure and Applied Chemistry, 2017
In this review we briefly discuss some new trends in the design of single molecule magnets based ... more In this review we briefly discuss some new trends in the design of single molecule magnets based on transition (3d, 4d, 5d) and rare-earth (4f) metal ions. Within this broad theme the emphasis of the present review is placed on the molecules which exhibit strong magnetic anisotropy originating from the unquenched orbital angular momenta in the ground orbitally degenerate (or quasi-degenerate) states. Along with the general concepts we consider selected examples of the systems comprising orbitally-degenerate metal ions and demonstrate how one can benefit from strong single-ion anisotropy arising from the first-order orbital angular momentum. The role of crystal fields, spin-orbit coupling and structural factors is discussed. Some observation stemming from the analysis of the isotropic exchange interactions, magnetic anisotropy and strongly anisotropic orbitally-dependent superexchange are summarized as guiding rules for the controlled design of single molecule magnets exhibiting high...
The measured Rabi oscillations of an ensemble of spins (here the spins 3/2 of the V15 single mole... more The measured Rabi oscillations of an ensemble of spins (here the spins 3/2 of the V15 single molecular magnet) are strongly damped by the excitation ac-field. The corresponding decoherence mechanism is attributed to an electromagnetic noise created by the dipolar spin-bath, inhomogeneously driven by the microwave field. Decoherence by electronic and nuclear spin-baths express themselves very differently vs microwave power. This decoherence mechanism should apply to all types of weakly interacting ensembles of qubits, beyond magnetism.
Physical Review B, 2014
The molecular compound K6[V IV 15 As III 6 O42(H2O)] • 8H2O, in short V15, has shown important qu... more The molecular compound K6[V IV 15 As III 6 O42(H2O)] • 8H2O, in short V15, has shown important quantum effects such as coherent spin oscillations. The details of the spin quantum dynamics depend on the exact form of the spin Hamiltonian. In this study, we present a precise analysis of the intramolecular interactions in V15. To that purpose, we performed high-field electron spin resonance measurements at 120 GHz and extracted the resonance fields as a function of crystal orientation and temperature. The data are compared against simulations using exact diagonalization to obtain the parameters of the molecular spin Hamiltonian.

In this article we analyze EPR and adiabatic magnetization of the nanoscopic V15 cluster exhibiti... more In this article we analyze EPR and adiabatic magnetization of the nanoscopic V15 cluster exhibiting a triangular V IV 3 array causing spin frustration. A model of V15 includes isotropic exchange interaction and antisymmetric (AS) exchange in the general form compatible with the trigonal symmetry. Orientation of the AS vector (but not its absolute value) is shown to play an important physical role in spin-frustrated systems. We were able to reach perfect fit to the experimental data on the stepwise dependence of magnetization vs. field at ultra-low temperatures. Furthermore, it was possible for the first time to estimate precisely two components of the AS vector coupling constant, namely, in-plane component and the perpendicular part. We show that only intramultiplet transitions in EPR are allowed when the vector of AS exchange is normal to the plane of vanadium triangle, meanwhile the in-plane part of AS exchange gives rise to a series of weak intermultiplet transitions. Experimenta...

Modern research in the area of mixed valency (MV) is focused on the nanosized clusters which are ... more Modern research in the area of mixed valency (MV) is focused on the nanosized clusters which are at the border between classical and quantum scales and for this reason they are particularly difficult to study. Due to mobility of the "extra" electron these systems are promising for a number of impressive applications in nanotechnology and especially in spintronics. Here, we describe a general approach to the evaluation of the energy pattern of MV systems containing arbitrary number of localized spins and itinerant electrons with due account for the double exchange and interelectronic Coulomb repulsion in instantly localized configurations. Then we present a symmetry adapted approach to the dynamic vibronic problem in large scale multimode molecular MV clusters and, more general, in Jahn-Teller (JT) systems. The developed techniques are applied to the analysis of the nanosized 2e-reduced MV Keggin anion in which the electronic pair is delocalized over twelve sites (point symmetry group T d ) giving rise to the ( 1 T 2 + 1 E+ 1 A 1 )(e+t 2 ) and ( 3 T 1 + 3 T 2 )(e+t 2 ) combined JT/pseudo JT problems for the spin-singlet and spin-triplet states. The delocalization of the two itinerant electrons in this remarkable systems was shown to lead to an effective spin paring. We study the energy pattern of this MV system and show that the JT vibronic interaction gives rise to a ferromagnetic contribution which proves to be in competition with the ferromagnetic coupling caused by the electron delocalization.
Chem. Sci., 2014
In delocalized magnetic mixed-valence molecules the spin-crossover induced by an electric field m... more In delocalized magnetic mixed-valence molecules the spin-crossover induced by an electric field may have a strong influence on their optical properties.
Advances in Quantum Chemistry, 2003
This chapter is dedicated to Professor Isaak Bersuker on the occasion of his 75th birthday -as a ... more This chapter is dedicated to Professor Isaak Bersuker on the occasion of his 75th birthday -as a sign of our appreciation of his outstanding contribution to the theory of the Jahn -Teller effect

The Journal of Physical Chemistry A, 2009
This article is a part of our efforts to control the magnetic anisotropy in cyanide-based exchang... more This article is a part of our efforts to control the magnetic anisotropy in cyanide-based exchange-coupled systems with the eventual goal to obtain single-molecule magnets with higher blocking temperatures. We give the theoretical interpretation of the magnetic properties of the new pentanuclear complex 3 Os III 2 cluster). Because the system contains the heavy Os III ions, spin-orbit coupling considerably exceeds the contributions from the low-symmetry crystal field and exchange coupling. The magnetic properties of the Ni II 3 Os III 2 cluster are described in the framework of a highly anisotropic pseudo-spin Hamiltonian that corresponds to the limit of strong spin-orbital coupling and takes into account the complex molecular structure. The model provides a good fit to the experimental data and allows the conclusion that the trigonal axis of the bipyramidal Ni II 3 Os III 2 cluster is a hard axis of magnetization. This explains the fact that in contrast with the isostructural trigonal bipyramidal Mn III 2 Mn II 3 cluster, the Ni II 3 Os III 2 system does not exhibit the single-molecule magnetic behavior.
Polyhedron, 2003
In this paper, the low lying levels of d 1 and low-spin d 5 metal complexes possessing ground 2 T... more In this paper, the low lying levels of d 1 and low-spin d 5 metal complexes possessing ground 2 T 2 term are considered. Strong spin Á/ orbital interactions is taken into account along with the axial (trigonal or tetragonal) component of the crystal field. In the framework of the semi-classic adiabatic approximation, vibronic Jahn Á/Teller and pseudo Jahn Á/Teller interactions acting within the ground manifold are also considered. The influence of the low-symmetry crystal fields, covalence reduction factor, spin Á/orbital and Jahn Á/Teller interactions on the anisotropy of g -factors, temperature independent paramagnetic contributions, and magnetic susceptibility is elucidated.

Physics Letters A, 2006
The magnetic three spin-1/2 model for nanometer-scale molecular cluster V 15 is analyzed with the... more The magnetic three spin-1/2 model for nanometer-scale molecular cluster V 15 is analyzed with the emphasis on the origin of the mixing of different spin levels in the resonance fields that is generally important for the problem of single molecular magnets. The zero-field splitting in the ground quadruplet (two S = 1/2 levels) is shown to depend mainly on the normal component of AS exchange meanwhile the zero-field splitting in the excited S = 3/2 multiplet is a second order effect with respect to in-plane components of AS exchange. The normal component of the AS exchange is shown to lead to the exact crossing of the magnetic sublevels at the arbitrary direction of the field. The positions of two crossing/anticrossing points in the ground manifold depend mainly on the isotropic exchange and normal component of AS exchange meanwhile the gap in the avoided crossing point in parallel field is affected only by the in-plane component. We discuss the role of AS exchange in the field and temperature dependence of the adiabatic magnetization. We predict a specific field dependence of the magnetization vs. field caused by AS exchange.
Physical Review B, 2008
We show that in molecular Ni 4 clusters with S 4 symmetry, not only the local anisotropy but also... more We show that in molecular Ni 4 clusters with S 4 symmetry, not only the local anisotropy but also the antisymmetric exchange interaction contributes to the observed fourth-order anisotropy terms in the single-spin Hamiltonian. From a group-theoretical classification of the exchange-coupled multiplets, the effective spin Hamiltonian terms are determined. We find that low-lying excited spin states possess an orbital angular momentum, which mixes into the spin ground state, leading to an effective antisymmetric exchange term. The simulation of the magnetic and spectroscopic experimental data allowed the extraction of parameter values for all interactions.
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Papers by Boris Tsukerblat