922 research outputs found
Revised self-consistent continuum solvation in electronic-structure calculations
The solvation model proposed by Fattebert and Gygi [Journal of Computational
Chemistry 23, 662 (2002)] and Scherlis et al. [Journal of Chemical Physics 124,
074103 (2006)] is reformulated, overcoming some of the numerical limitations
encountered and extending its range of applicability. We first recast the
problem in terms of induced polarization charges that act as a direct mapping
of the self-consistent continuum dielectric; this allows to define a functional
form for the dielectric that is well behaved both in the high-density region of
the nuclear charges and in the low-density region where the electronic
wavefunctions decay into the solvent. Second, we outline an iterative procedure
to solve the Poisson equation for the quantum fragment embedded in the solvent
that does not require multi-grid algorithms, is trivially parallel, and can be
applied to any Bravais crystallographic system. Last, we capture some of the
non-electrostatic or cavitation terms via a combined use of the quantum volume
and quantum surface [Physical Review Letters 94, 145501 (2005)] of the solute.
The resulting self-consistent continuum solvation (SCCS) model provides a very
effective and compact fit of computational and experimental data, whereby the
static dielectric constant of the solvent and one parameter allow to fit the
electrostatic energy provided by the PCM model with a mean absolute error of
0.3 kcal/mol on a set of 240 neutral solutes. Two parameters allow to fit
experimental solvation energies on the same set with a mean absolute error of
1.3 kcal/mol. A detailed analysis of these results, broken down along different
classes of chemical compounds, shows that several classes of organic compounds
display very high accuracy, with solvation energies in error of 0.3-0.4
kcal/mol, whereby larger discrepancies are mostly limited to self-dissociating
species and strong hydrogen-bond forming compounds.Comment: The following article has been accepted by The Journal of Chemical
Physics. After it is published, it will be found at
http://link.aip.org/link/?jcp
Continuous dielectric permittivity I: Specific features of the dielectric continuum solvation model with a position-dependent permittivity function
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 = 0 for the electric strength field E inherent to this
solution, which is the obligatory condition imposed by Maxwell equations. The
illustrative computation is made for the model system of the point dipole
immersed in a spherical cavity of excluded volume.Comment: 31 pages, 4 figure
The Poisson-Boltzmann model for implicit solvation of electrolyte solutions: Quantum chemical implementation and assessment via Sechenov coefficients.
We present the theory and implementation of a Poisson-Boltzmann implicit solvation model for electrolyte solutions. This model can be combined with arbitrary electronic structure methods that provide an accurate charge density of the solute. A hierarchy of approximations for this model includes a linear approximation for weak electrostatic potentials, finite size of the mobile electrolyte ions, and a Stern-layer correction. Recasting the Poisson-Boltzmann equations into Euler-Lagrange equations then significantly simplifies the derivation of the free energy of solvation for these approximate models. The parameters of the model are either fit directly to experimental observables-e.g., the finite ion size-or optimized for agreement with experimental results. Experimental data for this optimization are available in the form of Sechenov coefficients that describe the linear dependence of the salting-out effect of solutes with respect to the electrolyte concentration. In the final part, we rationalize the qualitative disagreement of the finite ion size modification to the Poisson-Boltzmann model with experimental observations by taking into account the electrolyte concentration dependence of the Stern layer. A route toward a revised model that captures the experimental observations while including the finite ion size effects is then outlined. This implementation paves the way for the study of electrochemical and electrocatalytic processes of molecules and cluster models with accurate electronic structure methods
Equilibrium solvation in quadrupolar solvents
We present a microscopic theory of equilibrium solvation in solvents with
zero dipole moment and non-zero quadrupole moment (quadrupolar solvents). The
theory is formulated in terms of autocorrelation functions of the quadrupolar
polarization (structure factors). It can be therefore applied to an arbitrary
dense quadrupolar solvent for which the structure factors are defined. We
formulate a simple analytical perturbation treatment for the structure factors.
The solute is described by coordinates, radii, and partial charges of
constituent atoms. The theory is tested on Monte Carlo simulations of solvation
in model quadrupolar solvents. It is also applied to the calculation of the
activation barrier of electron transfer reactions in a cleft-shaped
donor-acceptor complex dissolved in benzene with the structure factors of
quadrupolar polarization obtained from Molecular Dynamics simulations.Comment: Submitted to J. Chem. Phys., 20 pages and 13 figure
Theory of solvation in polar nematics
We develop a linear response theory of solvation of ionic and dipolar solutes
in anisotropic, axially symmetric polar solvents. The theory is applied to
solvation in polar nematic liquid crystals. The formal theory constructs the
solvation response function from projections of the solvent dipolar
susceptibility on rotational invariants. These projections are obtained from
Monte Carlo simulations of a fluid of dipolar spherocylinders which can exist
both in the isotropic and nematic phase. Based on the properties of the solvent
susceptibility from simulations and the formal solution, we have obtained a
formula for the solvation free energy which incorporates experimentally
available properties of nematics and the length of correlation between the
dipoles in the liquid crystal. Illustrative calculations are presented for the
Stokes shift and Stokes shift correlation function of coumarin-153 in
4-n-pentyl-4'-cyanobiphenyl (5CB) and 4,4-n-heptyl-cyanopiphenyl (7CB) solvents
as a function of temperature in both the nematic and isotropic phase.Comment: 19 pages, 9 figure
Hydration free energies of molecular ions from theory and simulation
We present a theoretical/computational framework for accurate calculation of hydration free energies of ionized molecular species. The method is based on a molecular theory, 3D-RISM, combined with a recently developed pressure correction (PC+). The 3D-RISM/PC+ model can provide âŒ3 kcal/mol hydration free energy accuracy for a large variety of ionic compounds, provided that the Galvani potential of water is taken into account. The results are compared with direct atomistic simulations. Several methodological aspects of hydration free energy calculations for charged species are discussed
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