arXiv subjects

Mikhail V. Ivanov

Publications and source records attributed to Mikhail V. Ivanov.

8 recordsLinked to original sources

arXiv2026

Dissociation of NaCl in supercritical aqueous fluids of moderate and high concentrations: A molecular dynamics study

We report classical molecular dynamics simulations of NaCl association and dissociation in supercritical aqueous fluids over a wide range of salt concentrations, from moderate salinity to highly concentrated H2O-NaCl mixtures attainable at high temperatures. The degree of dissociation a and the corresponding ideal dissociation constant Kd, derived directly from a, were calculated as functions of the stoichiometric NaCl mole fraction at selected pressure-temperature (PT) conditions from 673.15 to 1273.15 K and from 0.1 to 2 GPa. At moderate salinity corresponding to a molality of approximately 1 mol/kg, NaCl remains largely dissociated a = 0.3-0.7 depending on pressure and temperature). In contrast, when the mole fraction of NaCl increases up to xNaCl = 0.333 (27.8 mol/kg), the degree of dissociation tends towards zero, and most ions form Na$^+$Cl$^-$ contact pairs and multi-ion clusters. As a result of these competing trends, the mole fraction of structurally dissociated Na$^+$ and Cl$^-$ ions is a non-monotonic function of the stoichiometric NaCl concentration and typically reaches a maximum at xNaCl = 0.06-0.10. This result shows that increasing salinity does not necessarily increase the abundance of structurally available chloride ions in supercritical aqueous fluids. Additional fixed density simulations at 1 and 7 mol/kg extend the analysis up to 1673.15 K and separate the effects of temperature and density on the associate/dissociate state of the ions. The obtained concentration dependences provide molecular-level constraints for thermodynamic descriptions of concentrated supercritical electrolytes and for evaluating chloride availability in high-temperature aqueous fluids.

cond-mat.soft↗

arXiv2022

Thermodynamic model of the fluid system H2O-CO2-NaCl-CaCl2 at P-T parameters of the middle and lower crust

Based on the earlier obtained equations of state for the ternary systems H2O-CO2-CaCl2 and H2O-CO2-NaCl, an equation of state for the four-component fluid system H2O-CO2-NaCl-CaCl2 is derived in terms of the Gibbs excess free energy. A corresponding numerical thermodynamic model is build. The main part of the numerical parameters of the model coincides with the corresponding parameters of the ternary systems. The NaCl-CaCl2 interaction parameter was obtained from the experimental liquidus of the salt mixture. Similar to the thermodynamic models for H2O-CO2-CaCl2 and H2O-CO2-NaCl, the range of applicability of the model is pressure 1-20 kbar and temperature from 500C to 1400C. The model makes it possible to predict the physicochemical properties of the fluid involved in most processes of deep petrogenesis: the phase state of the system (homogeneous or multiphase fluid, presence or absence of solid salts), chemical activities of the components, densities of the fluid phases, and concentrations of the components in the coexisting phases. The model was used for a detailed study of the phase state and activity of water on the H2O-CO2-salt sections when changing the ratio xNaCl/(xNaCl+xCaCl2) from 1 to 0. Changes in the composition and density of coexisting fluid phases at a constant activity of water and changes in the total composition of the system are studied. A set of phase diagrams on sections H2O-NaCl-CaCl2 for different mole fractions of CO2 is obtained. Pressure dependencies of the maximal activity of water in the field of coexisting unmixable fluid phases are obtained for several salt compositions of the system. Due to removal of restrictions resulting from a smaller number of components in ternary systems, the thermodynamic behavior of systems with a mixed composition of the salt is significantly differ from the behavior of those with a single salt component.

physics.chem-ph↗

arXiv2017

Empirical model of the Gibbs free energy for saline solutions of arbitrary concentration: Application for H2O-NaCl solutions at 423.15K-573.15K and pressures from saturation up to 5kbar

An empirical model of the concentration dependence of the excess Gibbs free energy Gex for saline solutions is proposed. Our simple analytical form of Gex allows obtaining equations of state of saline solutions equally precise in the whole range of the salt concentrations, from dilute solutions up to the limit of solubility. Our equation for Gex includes one term responsible for concentration dependence of Gex at low salt concentrations and two terms of Margules type dependent on powers of mole fractions of the components. These terms contain four parameters dependent on temperature and pressure. As an example of application of the proposed model we took the system H2O-NaCl. For fixed T and P, our four-parameter form of Gex allows precisely reproduce experimental data for NaCl water solutions, including both regions of low and high concentrations. An introduction of temperature dependence of the parameters allowed us to build a precise analytic fit of experimental data on osmotic coefficients of NaCl solutions for saturation pressures of NaCl at temperatures 423.15K-573.15K. On the basis of PVTx data by Driesner (2007) the model was extended towards pressures up to 5kbar. Our form of Gex allows obtaining the molar volumes, activities of components and other thermodynamic properties of NaCl-H2O solutions in the range of temperatures 423.15K-573.15K and pressures from saturation up to 5kbar in the whole range of concentrations possible for H2O-NaCl solutions (from zero up to approximately 10 molal at 573.15K).

physics.chem-ph↗

arXiv2004

Impurity center in a semiconductor quantum ring in the presence of a radial electric field

The problem of an impurity electron in a quantum ring (QR) in the presence of a radially directed strong external electric field is investigated in detail. Both an analytical and a numerical approach to the problem are developed. The analytical investigation focuses on the regime of a strong wire-electric field compared to the electric field due to the impurity. An adiabatic and quasiclassical approximation is employed. The explicit dependencies of the binding energy of the impurity electron on the electric field strength, parameters of the QR and position of the impurity within the QR are obtained. Numerical calculations of the binding energy based on a finite-difference method in two and three dimensions are performed for arbitrary strengths of the electric field. It is shown that the binding energy of the impurity electron exhibits a maximum as a function of the radial position of the impurity that can be shifted arbitrarily by applying a corresponding wire-electric field. The maximal binding energy monotonically increases with increasing electric field strength. The inversion effect of the electric field is found to occur. An increase of the longitudinal displacement of the impurity typically leads to a decrease of the binding energy. Results for both low- and high-quantum rings are derived and discussed. Suggestions for an experimentally accessible set-up associated with the GaAs/GaAlAs QR are provided.

cond-mat.mes-hall↗

arXiv2002

Quantum phase transition in the Hartree-Fock wave function of the hydrogen molecule

Precise solutions of the Hartree-Fock equations for the ground state of the hydrogen molecule are obtained for a wide range of internuclear distances R by means of a two-dimensional fully numerical mesh computational method. The spatial parts of the single-electron wave functions are found to be coinciding for R<2.30a.u. At larger distances they become different and as R->\infty each of them takes the form corresponding to a separate atom. This quantum phase transition occurring at R=2.30a.u. gives a natural boundary between a delocalized behavior of electrons in the molecule and their distribution over separate atoms. This phenomenon can be also considered as an analog of the Wigner crystallization or the Mott transition on the level of a single molecule.

physics.atom-ph↗

arXiv2002

Two-dimensional negative donors in magnetic fields

A finite-difference solution of the Schroedinger equation for negative donor centers D^- in two dimensions is presented. Our approach is of exact nature and allows us to resolve a discrepancy in the literature on the ground state of a negative donor. Detailed calculations of the energies for a number of states show that for field strengths less than γ=0.117 a.u. the donor possesses one bound state, for 0.117<γ<1.68 a.u. there exist two bound states and for field strengths γ>1.68 a.u. the system possesses three bound states. Further relevant characteristics of negative donors in magnetic fields are provided.

cond-mat.mes-hall↗

arXiv2000

Multidimensional Mesh Approaches to Calculations of Atoms and Diatomic Molecules in Strong Electric Fields

Fully numerical mesh solutions of 2D and 3D quantum equations of Schroedinger and Hartree-Fock type allow us to work with wavefunctions which possess a very flexible geometry. This flexibility is especially important for calculations of atoms and molecules in strong external fields where neither the external field nor the internal interactions can be considered as a perturbation. In the framework of this method we present various approaches to calculations of quasi-steady states of these systems in strong electric fields. These approaches are aimed at obtaining precise complex wavefunctions and corresponding eigenvalues in the form E = E_0 - iΓ/2, where E_0 is the real part of the energy and the value Γ/2 determines the lifetime of the state in relation to escape of electrons from the system. The applications for single-electron systems include correct solutions of the Schroedinger equation for the H_2^+ ion (energies and decay rates) and the hydrogen atom in strong parallel electric and magnetic fields. Some results for the helium atom in strong electric fields are announced.

physics.atom-ph↗

arXiv2000

Finite-Difference Calculations for Atoms and Diatomic Molecules in Strong Magnetic and Static Electric Fields

Fully numerical mesh solutions of 2D quantum equations of Schroedinger and Hartree-Fock type allow us to work with wavefunctions which possess a very flexible geometry. This flexibility is especially important for calculations of atoms and molecules in strong external fields where neither the external field nor the internal interactions can be considered as a perturbation. The applications of the present approach include calculations of atoms and diatomic molecules in strong static electric and magnetic fields. For the latter we have carried out Hartree-Fock calculations for He, Li, C and several other atoms. This yields in particular the first comprehensive investigation of the ground state configurations of the Li and C atoms in the whole range of magnetic fields (0<B<10000 a.u.) and a study of the ground state electronic configurations of all the atoms with 1<Z<11 and their ions A^+ in the high-field fully spin-polarised regime. The results in a case of a strong electric field relate to single-electron systems including the correct solution of the Schroedinger equation for the H_2^+ ion (energies and decay rates) and the hydrogen atom in strong parallel electric and magnetic fields.

physics.atom-ph↗