M. Basilevsky - Academia.edu (original) (raw)
Papers by M. Basilevsky
An earlier developed Smooth Boundary Continuum Model (SBCM) which allows to consider the solution... more An earlier developed Smooth Boundary Continuum Model (SBCM) which allows to consider the solution in inhomogeneous media has been parameterized for the calculation of hydration free energy. The traditional (for implicit models of solvent influence) decomposition DG solv on polar, nonpolar and hydrophobic components for implicit models of solvent has been used. The peculiarity of SBCM appears as a positiondependent dielectric permittivity function, which is applied for a computation of the electrostatic component of DG solv in the frame of solving the pertaining Poisson equation. By this means non-uniformity of medium environment for a solute particle can be simulated. This feature distinguishes the present approach from its conventional counterparts based on standard uniform electrostatic schemes.
The Journal of Physical Chemistry B, 2002
The linearized MD technique is developed in order to treat systematically free energies of simple... more The linearized MD technique is developed in order to treat systematically free energies of simple charged and dipolar solutes in water. The solvent electrostatic response field in the solute region is modeled by averaging instantaneous fields found in a MD computation for solvent configurations confined within a cavity that conforms to the real shape of the solute particle. At this stage, all electrostatic interactions are explicitly treated inside the cavity. The solvent in the external region (outside the cavity) is modeled in terms of a standard continuum theory. For nonspherical cavities, the present approach is more accurate than the field computation employed at the preceding MD stage, where spherically truncated Coulomb potentials are modified by the reaction field corrections. We considered two different linearization schemes based on a computation of either the average response field or of its fluctuations. Only the first algorithm proved to be successful. For a series of single-charged monatomic cations and anions, it provides free energies that deviate by few percent from those found in full MD computations. The results are stable relative to a separation of the whole space occupied by the solvent into explicit solvent region (inside the cavity) and the continuum region (outside the cavity). The two-site dipolar dumbbell system was also studied in the range of intersite separation D within 2 Å < D < 10 Å. At the stage of the field computation, three different types of its solvation shell were considered: spherical and bispherical cavities and periodic solvent environment monitored in terms of Ewald method. Free solvation energies are the same (within 1 kcal/mol) for all three models. A smooth dependence of the mean field potential is observed as a function of separation D but its asymptotic value differs by 4 kcal/mol from the free energy computed for the isolated ion pair. The results generally agree with those obtained in the literature in terms of full MD simulations.
Journal of Physical Chemistry A, 1999
Time correlation functions describing the solvent relaxation around a molecule of coumarin-153 an... more Time correlation functions describing the solvent relaxation around a molecule of coumarin-153 and a benzophenone anion in acetonitrile are calculated using dynamical continuum theories of solvation with an experimental dielectric function (ω) including the resonance absorption region of the solvent. Apart from the local model with a single molecular-shaped solute cavity of the solute studied previously, a new dynamic local model with a double molecular-shaped cavity and a dynamic nonlocal theory with a spherical cavity are presented, both of which introduce elements of solvent structure. It is shown that both local models, one-and two-cavity, exhibit experimentally unobserved oscillations in the shorter time region t < 1 ps, although the experimental asymptote for t > 1 ps for coumarin is obtained. The dynamics of the two-cavity model are not seen to differ from those of the one-cavity model. The nonlocal dynamic theory is shown to be able to suppress these oscillations, but the long-time asymptote differs markedly from that of the local theories. The nature of this asymptote is studied analytically. *
Russian Chemical Reviews, 2003
Erratum to the article by M V Basilevsky, M V Vener 'Theoretical investigations of proton and hyd... more Erratum to the article by M V Basilevsky, M V Vener 'Theoretical investigations of proton and hydrogen atom transfer in the condensed phase', Russian Chemical Reviews, 72 1-33 (2003) This content has been downloaded from IOPscience. Please scroll down to see the full text.
Russian Chemical Reviews, 2003
Theoretical studies of the dynamics and kinetics of Theoretical studies of the dynamics and kinet... more Theoretical studies of the dynamics and kinetics of Theoretical studies of the dynamics and kinetics of proton and hydrogen atom transfer processes occupy a special proton and hydrogen atom transfer processes occupy a special place in the kinetics of chemical reactions. The transition state place in the kinetics of chemical reactions. The transition state theory is often inapplicable to these processes due to substantial theory is often inapplicable to these processes due to substantial quantum effects. Different approaches to the description of these quantum effects. Different approaches to the description of these reactions are discussed and compared. Calculations for a number reactions are discussed and compared. Calculations for a number of particular condensed-phase reactions involving proton or of particular condensed-phase reactions involving proton or hydrogen atom transfer are analysed. Data of calculations of hydrogen atom transfer are analysed. Data of calculations of potential energy surfaces for the considered systems and the potential energy surfaces for the considered systems and the results of experimental kinetic and spectroscopic studies are results of experimental kinetic and spectroscopic studies are presented. The bibliography includes 469 references presented. The bibliography includes 469 references. .
The Journal of Chemical Physics, 1998
The Journal of Chemical Physics, 1999
The Journal of Chemical Physics, 2003
The combined molecular-continuum approach developed in the preceding paper was applied for calcul... more The combined molecular-continuum approach developed in the preceding paper was applied for calculations of equilibrium solvation energies for a large number of polyatomic ions. The structure and charge distribution of the given ion were computed using the restricted Hartree-Fock level with the 6-31G** basis set. The standard Lennard-Jones ͑LJ͒ parameters, which were not specially calibrated to fit the solvation energies, were used in molecular dynamics simulations. Water ͑the SPC model͒ was considered as a solvent. The computations show that the new scheme works satisfactorily for nitrogen cations in the frame of a standard parametrization and can be further improved for oxygen ions by tuning solute-solvent LJ parameters. The calculated relative change of the energies in families of similar cations-i.e., ammonium-type or oxonium-type cations-fits the experimental trends. The present approach is specially addressed to separate the inertial contribution to solvation free energies, which is important in view of further applications to electron transfer reactions. Computed values of the inertial contribution to solvation energies of the ions and reorganization energies for the model two-site dumbbell system are found to be systematically lower than those obtained in terms of the standard treatments ͑using the Pekar factor or the polarizable continuum model ͑PCM͒͒.
The Journal of Chemical Physics, 2003
The hybrid molecular-continuum model for polar solvation considered in this paper combines the di... more The hybrid molecular-continuum model for polar solvation considered in this paper combines the dielectric continuum approximation for treating fast electronic ͑inertialess͒ polarization effects and a molecular dynamics ͑MD͒ simulation for the slow ͑inertial͒ polarization component, including orientational and translational solvent modes. The inertial polarization is generated by average charge distributions of solvent particles, composed of permanent and induced ͑electronic͒ components. MD simulations are performed in a manner consistent with the choice of solvent and solute charges such that all electrostatic interactions are scaled by the factor 1/ ϱ , where ϱ is the optical dielectric permittivity. This approach yields an ensemble of equilibrium solvent configurations adjusted to the electric field created by a charged or strongly polar solute. The electrostatic solvent response field is found as the solution of the Poisson equation including both solute and explicit solvent charges, with accurate account of electrostatic boundary conditions at the surfaces separating spatial regions with different dielectric permittivities. Both equilibrium and nonequilibrium solvation effects can be studied by means of this model, and their inertial and inertialess contributions are naturally separated. The methodology for computation of charge transfer reorganization energies is developed and applied to a model two-site dipolar system in the SPC water solvent. Three types of charge transfer reactions are considered. The standard linear-response approach yields high accuracy for each particular reaction, but proves to be significantly in error when reorganization energies of different reactions were compared. This result has a purely molecular origin and is absent within a conventional continuum solvent model.
The Journal of Chemical Physics, 2009
A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the ... more A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the density functional theory. The presence of two variables, namely, the dimensionless solvent composition y and the dimensionless total solvent density z, is an essential feature of binary systems. Their coupling, hidden in the structure of the local dielectric permittivity function, is postulated at the phenomenological level. Local equilibrium conditions are derived by a variation in the free energy functional expressed in terms of the composition and density variables. They appear as a pair of coupled equations defining y and z as spatial distributions. We consider the simplest spherically symmetric case of the Born-type ion immersed in the benzene/dimethylsulfoxide (DMSO) solvent mixture. The profiles of y(R) and z(R) along the radius R, which measures the distance from the ion center, are found in molecular dynamics (MD) simulations. It is shown that for a given solute ion z(R) does not depend significantly on the composition variable y. A simplified solution is then obtained by inserting z(R), found in the MD simulation for the pure DMSO, in the single equation which defines y(R). In this way composition dependences of the main solvation effects are investigated. The local density augmentation appears as a peak of z(R) at the ion boundary. It is responsible for the fine solvation effects missing when the ordinary solvation theories, in which z=1, are applied. These phenomena, studied for negative ions, reproduce consistently the simulation results. For positive ions the simulation shows that z&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;1 (z=5-6 at the maximum of the z peak), which means that an extremely dense solvation shell is formed. In such a situation the continuum description fails to be valid within a consistent parametrization.
Chemical Physics, 1980
ABSTRACT The natural reaction coordinates (NRC) are not well suitable for the dynamical investiga... more ABSTRACT The natural reaction coordinates (NRC) are not well suitable for the dynamical investigation of the transfer of the light atom in chemical exchange reactions. In this case the curvature of the reaction coordinate is large and the probability flux gets across the region of multi-valuedness of the NRC. We introduce a new coordinate system (the matching coordinates, MC), that are specially adapted for the reactions with large curvature, and suggest a new method for solving equations of motion in those coordinates. The multi-valuedness is eliminated by drawing a cut from the centre of maximum curvature of the reaction coordinate curve. Matching of the wavefunction and its normal derivative is performed along the cut. The matching conditions play the role of the operator that is responsible for the direct interaction between the reactant and product regions of a potential energy surface and promotes nonadiabatic transitions between them. The matrix Schrödinger equation for the translational motion is converted into a form that can be solved by the previously elaborated effective procedure. The construction of the scattering matrix for this problem, involving equations of motion with constraints (the matching conditions), needs a special projection technique.
Chemical Physics, 2000
A method of calculation of a free-energy surface (FES) of the proton transfer (PT) reaction in a ... more A method of calculation of a free-energy surface (FES) of the proton transfer (PT) reaction in a polar aprotic solvent is developed. This is based on the two-state (valence bond) VB description of the solute combined with recent continuum medium models. Its essential new feature is an explicit quantum-chemical treatment of VB wave functions, including internal electronic structure of a chemical subsystem. The FES includes a pair of intrasolute coordinates, R, the distance between hydrogen-bonded atoms and s, the proton coordinate, together with the collective medium polarization mode. Two hydrogen-bonded systems immersed in a polar solvent (Freon) were considered. The ®rst one is the H 5 O 2 ion, a model system which was used as a benchmark testifying the validity of our semiempirical calculations. The second system is the neutral (CN)(CH 3 )N±HÁ Á ÁN(CH 3 ) 3 complex in Freon. PT for this system has been studied experimentally. The dependencies of basic parameters controlling FES properties (the overlap integral, the coupling matrix element and the reorganization energy E r ) on intrasolute coordinates R and s are evaluated and discussed. In particular, for the neutral complex, E r depends on s linearly, and its dependence on R is weak. The FES, for the neutral system, has two potential wells separated by the energy barrier of $7 kcal/mol. Quantum-mechanical averaging over the proton coordinate, s, reduces the barrier from 7.0 to 1.2 kcal/mol. The value of the nonadiabatic parameter on the averaged FES is equal to 0.13. This implies that the PT in the second system corresponds to an intermediate dynamic regime and that proton tunneling eects are hardly signi®cant for this reaction. Ó
Chemical Physics, 2005
Outersphere reorganization energies (k) for intramolecular electron transfer (ET) and hole transf... more Outersphere reorganization energies (k) for intramolecular electron transfer (ET) and hole transfer are studied in anion-and cation-radical forms of complex organic substrates (biphenylyl-spacer-naphtyl) in polar solvents simulated by means of the nonpolarizable models of water and 1,2-dichloroethane. The earlier elaborated molecular/continuum approach (the MD/FRCM, J. Chem. Phys., 119 (2003) 8024) is used; this method provides a physically relevant background for separating inertial and inertialess polarization responses within a nonpolarizable MD simulation (the SPC water model). Quantum-chemical calculations of solute charge distributions were performed with semiempirical (AM1) and second ab initio (HF/6-31G(d,p)) approximations. Ab initio charges give lower k-values and are preferable, probably, because of including the effect of the SCRF polarization of the diabatic ET states. Standard Lennard-Jones and charge parameters implemented in MD runs were not specially fitted for reproducing ET effects. The difference in values for a cation and an anion originating from the same parent structure was specially investigated. As shown earlier, this effect, nonlinear in its nature, proved to be extremely large when a model dipolar two-site system was studied. For the present ET structures representing real chemical substrates it has reduced to a plausible value of 6-8 kcal/mol. The study of the temperature dependence of k comprises a first MD simulation of this problem and its slope was found to be in accord with an experimental observation for an anionic species. Calculations of absolute k-values for the hole transfer in 1,2-dichloroethane are the first MD simulations of reorganization energies in experimentally studied reactions. Computed values of k-s are higher than the experimental data. The effect of this magnitude could be eliminated by proper tuning the solvent parameters.
Chemical Physics, 1986
An approximate method for calculating the probabilities of linear reactions of a light-atom trans... more An approximate method for calculating the probabilities of linear reactions of a light-atom transfer based on the Born distorted-wave approximation is proposed. The matrix element over the vibrational coordinate is numerically calculated, the translational motion is treated quasi-classically. The reaction probability expressed as a triple integral is evaluated by the steepest descent method. All the integrands are expanded at the saddle point, its position being determined by iterations. Complete quantum calculations are compared with this model treatment for the following reactions: CH; +CH,, CH; + PhCH,, CH; + PhCH,D.
We consider a modified formulation for the recently developed new approach in the continuum solva... more We consider a modified formulation for the recently developed new approach in the continuum solvation theory (Basilevsky, M. V., Grigoriev, F. V., Nikitina, E. A., Leszczynski, J., J. Phys. Chem. B 2010, 114, 2457), which is based on the exact solution of the electrostatic Poisson equation with the space-dependent dielectric permittivity. Its present modification ensures the property curl E =
An earlier developed Smooth Boundary Continuum Model (SBCM) which allows to consider the solution... more An earlier developed Smooth Boundary Continuum Model (SBCM) which allows to consider the solution in inhomogeneous media has been parameterized for the calculation of hydration free energy. The traditional (for implicit models of solvent influence) decomposition DG solv on polar, nonpolar and hydrophobic components for implicit models of solvent has been used. The peculiarity of SBCM appears as a positiondependent dielectric permittivity function, which is applied for a computation of the electrostatic component of DG solv in the frame of solving the pertaining Poisson equation. By this means non-uniformity of medium environment for a solute particle can be simulated. This feature distinguishes the present approach from its conventional counterparts based on standard uniform electrostatic schemes.
The Journal of Physical Chemistry B, 2002
The linearized MD technique is developed in order to treat systematically free energies of simple... more The linearized MD technique is developed in order to treat systematically free energies of simple charged and dipolar solutes in water. The solvent electrostatic response field in the solute region is modeled by averaging instantaneous fields found in a MD computation for solvent configurations confined within a cavity that conforms to the real shape of the solute particle. At this stage, all electrostatic interactions are explicitly treated inside the cavity. The solvent in the external region (outside the cavity) is modeled in terms of a standard continuum theory. For nonspherical cavities, the present approach is more accurate than the field computation employed at the preceding MD stage, where spherically truncated Coulomb potentials are modified by the reaction field corrections. We considered two different linearization schemes based on a computation of either the average response field or of its fluctuations. Only the first algorithm proved to be successful. For a series of single-charged monatomic cations and anions, it provides free energies that deviate by few percent from those found in full MD computations. The results are stable relative to a separation of the whole space occupied by the solvent into explicit solvent region (inside the cavity) and the continuum region (outside the cavity). The two-site dipolar dumbbell system was also studied in the range of intersite separation D within 2 Å < D < 10 Å. At the stage of the field computation, three different types of its solvation shell were considered: spherical and bispherical cavities and periodic solvent environment monitored in terms of Ewald method. Free solvation energies are the same (within 1 kcal/mol) for all three models. A smooth dependence of the mean field potential is observed as a function of separation D but its asymptotic value differs by 4 kcal/mol from the free energy computed for the isolated ion pair. The results generally agree with those obtained in the literature in terms of full MD simulations.
Journal of Physical Chemistry A, 1999
Time correlation functions describing the solvent relaxation around a molecule of coumarin-153 an... more Time correlation functions describing the solvent relaxation around a molecule of coumarin-153 and a benzophenone anion in acetonitrile are calculated using dynamical continuum theories of solvation with an experimental dielectric function (ω) including the resonance absorption region of the solvent. Apart from the local model with a single molecular-shaped solute cavity of the solute studied previously, a new dynamic local model with a double molecular-shaped cavity and a dynamic nonlocal theory with a spherical cavity are presented, both of which introduce elements of solvent structure. It is shown that both local models, one-and two-cavity, exhibit experimentally unobserved oscillations in the shorter time region t < 1 ps, although the experimental asymptote for t > 1 ps for coumarin is obtained. The dynamics of the two-cavity model are not seen to differ from those of the one-cavity model. The nonlocal dynamic theory is shown to be able to suppress these oscillations, but the long-time asymptote differs markedly from that of the local theories. The nature of this asymptote is studied analytically. *
Russian Chemical Reviews, 2003
Erratum to the article by M V Basilevsky, M V Vener 'Theoretical investigations of proton and hyd... more Erratum to the article by M V Basilevsky, M V Vener 'Theoretical investigations of proton and hydrogen atom transfer in the condensed phase', Russian Chemical Reviews, 72 1-33 (2003) This content has been downloaded from IOPscience. Please scroll down to see the full text.
Russian Chemical Reviews, 2003
Theoretical studies of the dynamics and kinetics of Theoretical studies of the dynamics and kinet... more Theoretical studies of the dynamics and kinetics of Theoretical studies of the dynamics and kinetics of proton and hydrogen atom transfer processes occupy a special proton and hydrogen atom transfer processes occupy a special place in the kinetics of chemical reactions. The transition state place in the kinetics of chemical reactions. The transition state theory is often inapplicable to these processes due to substantial theory is often inapplicable to these processes due to substantial quantum effects. Different approaches to the description of these quantum effects. Different approaches to the description of these reactions are discussed and compared. Calculations for a number reactions are discussed and compared. Calculations for a number of particular condensed-phase reactions involving proton or of particular condensed-phase reactions involving proton or hydrogen atom transfer are analysed. Data of calculations of hydrogen atom transfer are analysed. Data of calculations of potential energy surfaces for the considered systems and the potential energy surfaces for the considered systems and the results of experimental kinetic and spectroscopic studies are results of experimental kinetic and spectroscopic studies are presented. The bibliography includes 469 references presented. The bibliography includes 469 references. .
The Journal of Chemical Physics, 1998
The Journal of Chemical Physics, 1999
The Journal of Chemical Physics, 2003
The combined molecular-continuum approach developed in the preceding paper was applied for calcul... more The combined molecular-continuum approach developed in the preceding paper was applied for calculations of equilibrium solvation energies for a large number of polyatomic ions. The structure and charge distribution of the given ion were computed using the restricted Hartree-Fock level with the 6-31G** basis set. The standard Lennard-Jones ͑LJ͒ parameters, which were not specially calibrated to fit the solvation energies, were used in molecular dynamics simulations. Water ͑the SPC model͒ was considered as a solvent. The computations show that the new scheme works satisfactorily for nitrogen cations in the frame of a standard parametrization and can be further improved for oxygen ions by tuning solute-solvent LJ parameters. The calculated relative change of the energies in families of similar cations-i.e., ammonium-type or oxonium-type cations-fits the experimental trends. The present approach is specially addressed to separate the inertial contribution to solvation free energies, which is important in view of further applications to electron transfer reactions. Computed values of the inertial contribution to solvation energies of the ions and reorganization energies for the model two-site dumbbell system are found to be systematically lower than those obtained in terms of the standard treatments ͑using the Pekar factor or the polarizable continuum model ͑PCM͒͒.
The Journal of Chemical Physics, 2003
The hybrid molecular-continuum model for polar solvation considered in this paper combines the di... more The hybrid molecular-continuum model for polar solvation considered in this paper combines the dielectric continuum approximation for treating fast electronic ͑inertialess͒ polarization effects and a molecular dynamics ͑MD͒ simulation for the slow ͑inertial͒ polarization component, including orientational and translational solvent modes. The inertial polarization is generated by average charge distributions of solvent particles, composed of permanent and induced ͑electronic͒ components. MD simulations are performed in a manner consistent with the choice of solvent and solute charges such that all electrostatic interactions are scaled by the factor 1/ ϱ , where ϱ is the optical dielectric permittivity. This approach yields an ensemble of equilibrium solvent configurations adjusted to the electric field created by a charged or strongly polar solute. The electrostatic solvent response field is found as the solution of the Poisson equation including both solute and explicit solvent charges, with accurate account of electrostatic boundary conditions at the surfaces separating spatial regions with different dielectric permittivities. Both equilibrium and nonequilibrium solvation effects can be studied by means of this model, and their inertial and inertialess contributions are naturally separated. The methodology for computation of charge transfer reorganization energies is developed and applied to a model two-site dipolar system in the SPC water solvent. Three types of charge transfer reactions are considered. The standard linear-response approach yields high accuracy for each particular reaction, but proves to be significantly in error when reorganization energies of different reactions were compared. This result has a purely molecular origin and is absent within a conventional continuum solvent model.
The Journal of Chemical Physics, 2009
A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the ... more A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the density functional theory. The presence of two variables, namely, the dimensionless solvent composition y and the dimensionless total solvent density z, is an essential feature of binary systems. Their coupling, hidden in the structure of the local dielectric permittivity function, is postulated at the phenomenological level. Local equilibrium conditions are derived by a variation in the free energy functional expressed in terms of the composition and density variables. They appear as a pair of coupled equations defining y and z as spatial distributions. We consider the simplest spherically symmetric case of the Born-type ion immersed in the benzene/dimethylsulfoxide (DMSO) solvent mixture. The profiles of y(R) and z(R) along the radius R, which measures the distance from the ion center, are found in molecular dynamics (MD) simulations. It is shown that for a given solute ion z(R) does not depend significantly on the composition variable y. A simplified solution is then obtained by inserting z(R), found in the MD simulation for the pure DMSO, in the single equation which defines y(R). In this way composition dependences of the main solvation effects are investigated. The local density augmentation appears as a peak of z(R) at the ion boundary. It is responsible for the fine solvation effects missing when the ordinary solvation theories, in which z=1, are applied. These phenomena, studied for negative ions, reproduce consistently the simulation results. For positive ions the simulation shows that z&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;1 (z=5-6 at the maximum of the z peak), which means that an extremely dense solvation shell is formed. In such a situation the continuum description fails to be valid within a consistent parametrization.
Chemical Physics, 1980
ABSTRACT The natural reaction coordinates (NRC) are not well suitable for the dynamical investiga... more ABSTRACT The natural reaction coordinates (NRC) are not well suitable for the dynamical investigation of the transfer of the light atom in chemical exchange reactions. In this case the curvature of the reaction coordinate is large and the probability flux gets across the region of multi-valuedness of the NRC. We introduce a new coordinate system (the matching coordinates, MC), that are specially adapted for the reactions with large curvature, and suggest a new method for solving equations of motion in those coordinates. The multi-valuedness is eliminated by drawing a cut from the centre of maximum curvature of the reaction coordinate curve. Matching of the wavefunction and its normal derivative is performed along the cut. The matching conditions play the role of the operator that is responsible for the direct interaction between the reactant and product regions of a potential energy surface and promotes nonadiabatic transitions between them. The matrix Schrödinger equation for the translational motion is converted into a form that can be solved by the previously elaborated effective procedure. The construction of the scattering matrix for this problem, involving equations of motion with constraints (the matching conditions), needs a special projection technique.
Chemical Physics, 2000
A method of calculation of a free-energy surface (FES) of the proton transfer (PT) reaction in a ... more A method of calculation of a free-energy surface (FES) of the proton transfer (PT) reaction in a polar aprotic solvent is developed. This is based on the two-state (valence bond) VB description of the solute combined with recent continuum medium models. Its essential new feature is an explicit quantum-chemical treatment of VB wave functions, including internal electronic structure of a chemical subsystem. The FES includes a pair of intrasolute coordinates, R, the distance between hydrogen-bonded atoms and s, the proton coordinate, together with the collective medium polarization mode. Two hydrogen-bonded systems immersed in a polar solvent (Freon) were considered. The ®rst one is the H 5 O 2 ion, a model system which was used as a benchmark testifying the validity of our semiempirical calculations. The second system is the neutral (CN)(CH 3 )N±HÁ Á ÁN(CH 3 ) 3 complex in Freon. PT for this system has been studied experimentally. The dependencies of basic parameters controlling FES properties (the overlap integral, the coupling matrix element and the reorganization energy E r ) on intrasolute coordinates R and s are evaluated and discussed. In particular, for the neutral complex, E r depends on s linearly, and its dependence on R is weak. The FES, for the neutral system, has two potential wells separated by the energy barrier of $7 kcal/mol. Quantum-mechanical averaging over the proton coordinate, s, reduces the barrier from 7.0 to 1.2 kcal/mol. The value of the nonadiabatic parameter on the averaged FES is equal to 0.13. This implies that the PT in the second system corresponds to an intermediate dynamic regime and that proton tunneling eects are hardly signi®cant for this reaction. Ó
Chemical Physics, 2005
Outersphere reorganization energies (k) for intramolecular electron transfer (ET) and hole transf... more Outersphere reorganization energies (k) for intramolecular electron transfer (ET) and hole transfer are studied in anion-and cation-radical forms of complex organic substrates (biphenylyl-spacer-naphtyl) in polar solvents simulated by means of the nonpolarizable models of water and 1,2-dichloroethane. The earlier elaborated molecular/continuum approach (the MD/FRCM, J. Chem. Phys., 119 (2003) 8024) is used; this method provides a physically relevant background for separating inertial and inertialess polarization responses within a nonpolarizable MD simulation (the SPC water model). Quantum-chemical calculations of solute charge distributions were performed with semiempirical (AM1) and second ab initio (HF/6-31G(d,p)) approximations. Ab initio charges give lower k-values and are preferable, probably, because of including the effect of the SCRF polarization of the diabatic ET states. Standard Lennard-Jones and charge parameters implemented in MD runs were not specially fitted for reproducing ET effects. The difference in values for a cation and an anion originating from the same parent structure was specially investigated. As shown earlier, this effect, nonlinear in its nature, proved to be extremely large when a model dipolar two-site system was studied. For the present ET structures representing real chemical substrates it has reduced to a plausible value of 6-8 kcal/mol. The study of the temperature dependence of k comprises a first MD simulation of this problem and its slope was found to be in accord with an experimental observation for an anionic species. Calculations of absolute k-values for the hole transfer in 1,2-dichloroethane are the first MD simulations of reorganization energies in experimentally studied reactions. Computed values of k-s are higher than the experimental data. The effect of this magnitude could be eliminated by proper tuning the solvent parameters.
Chemical Physics, 1986
An approximate method for calculating the probabilities of linear reactions of a light-atom trans... more An approximate method for calculating the probabilities of linear reactions of a light-atom transfer based on the Born distorted-wave approximation is proposed. The matrix element over the vibrational coordinate is numerically calculated, the translational motion is treated quasi-classically. The reaction probability expressed as a triple integral is evaluated by the steepest descent method. All the integrands are expanded at the saddle point, its position being determined by iterations. Complete quantum calculations are compared with this model treatment for the following reactions: CH; +CH,, CH; + PhCH,, CH; + PhCH,D.
We consider a modified formulation for the recently developed new approach in the continuum solva... more We consider a modified formulation for the recently developed new approach in the continuum solvation theory (Basilevsky, M. V., Grigoriev, F. V., Nikitina, E. A., Leszczynski, J., J. Phys. Chem. B 2010, 114, 2457), which is based on the exact solution of the electrostatic Poisson equation with the space-dependent dielectric permittivity. Its present modification ensures the property curl E =