F.J.Olivares del Valle

Nonequilibrium solvation: An ab initio quantum‐mechanical method in the continuum cavity model approximation

The electrostatic relationships necessary for the quantum‐mechanical evaluation of the properties of a solute experiencing sudden changes in its internal charge distribution are here presented in a form suitable to perform accurate quantum‐mechanical calculations of the solute properties. Attention has been paid to express the boundary conditions in the most convenient form and to avoid further constraints on the elaboration of the computational procedures. The approach exploits the separation of orientational (inertial) and electronic (inertialess) components of the polarization and complements the polarizable continuum method [Chem. Phys. 65, 239 (1982)], usually employed for static descriptions. Examples of application of the method to photoionization and electronic transitions processes are shown.

Electron correlation and solvation effects. I, Basic formulation and preliminary attempt to include the electron correlation in the quantum mechanical polarizable continuum model so as to study solvation phenomena

Abstract In this paper we present a formulation of the Polarizable Continuum Model including the consideration of the electron correlation. Three levels of complexity in the method are considered, the first two introducing a partial decoupling of solvation and correlation effects. Third order calculations show a clear influence of electron correlation on the solvation energy and parallel influence of solvent polarization effects on the correlation energy. The analysis has been performed over a representative set of solutes, also taking into consideration the most significant observables.

Study of solvent effects by means of averaged solvent electrostatic potentials obtained from molecular dynamics data

We present the theory and implementation of a new approach for studying solvent effects. The electronic structure of the solute, calculated at the ab initio level, is obtained in the presence of the surrounding medium. We employ a mean field theory in which the solvent response is described by means of point charges chosen in such a way that they reproduce the average value of the solvent electrostatic potential calculated from molecular dynamics data. In this way, the complete solvent potential can be introduced into the solute Hamiltonian without making use of a one‐center multiple expansion of the solute‐solvent potential. In the proposed method, only one quantum calculation has to be performed and a great number of configurations can easily be included making the calculation statistically significant. We show that, despite the large fluctuations in the solute charge distribution induced by the solvent, the proposed mean field theory adequately reproduces the energetics and properties of formamide and water molecules in aqueous solution.

A multiconfiguration self-consistent field/molecular dynamics study of the (n→π*)1 transition of carbonyl compounds in liquid water

A model is presented for the electrostatic component of solvatochromic shifts in vertical electronic excitation energies. The model, which makes use of the mean-field approximation, combines quantum mechanics (QM) in the description of the solute molecule and molecular mechanics (MM) in the description of the solvent. The method is implemented at the multiconfigurational self-consistent field level. We present illustrative applications to the (n→π*)1 transitions of formaldehyde, acetaldehyde, and acetone in liquid water. The solvent shifts obtained compare well with other ab initio QM/MM calculations and when the electron correlation components are included with the experimental solvent shift, but differ from the results obtained with semiempirical QM/MM and continuum models.

Geometry optimization of molecules in solution: Joint use of the mean field approximation and the free-energy gradient method

The average solvent electrostatic potential/molecular dynamics (ASEP/MD) and the free-energy gradient methods are applied together with the multidimensional geometry optimization of molecules in solution. The systems studied were formamide in aqueous solution and water and methanol in liquid phase. The solute molecules were described through ab initio quantum mechanics methods (density dunctional theory or Moller–Plesset second order perturbation theory) while the solvent structure was obtained from Molecular Dynamics calculations. The method is very efficient; the increase in computation time is minimal with respect to previous ASEP/MD versions that worked at a fixed geometry. Despite the use of the mean field approximation in the calculation of the solvent reaction potential the agreement with previous theoretical calculations was satisfactory. Large changes were observed in the solute charge distribution induced by the solvent, and the solute polarization was accompanied by an increase in the solvent s...

Solute-solvent interactions. a simple procedure for constructing the solvent cavity for retaining a molecular solute

Abstract The objective of this work is to propose a procedure for the adaptation of the molecular solute cavity size in a solvent, when we use the SCF LCAO MO treatment of solute-solvent interactions, following the continuum model. The atoms studied are H, Li, Be, C, N, O, F, NA, Mg, Si, P, and Cl. For all of them we find a functional dependence of the radii on the net charge considering the effect of electronic cloud and the basis set. The obtained formulae were used to compute the internal and electrostatic free energy changes in solvation processes, using the Tomasi model.

ASEP/MD: A program for the calculation of solvent effects combining QM/MM methods and the mean field approximation ☆

ASEP/MD is a computer program designed to implement the Averaged Solvent Electrostatic Potential/Molecular Dynamics (ASEP/MD) method developed by our group. It can be used for the study of solvent effects and properties of molecules in their liquid state or in solution. It is written in the FORTRAN90 programming language, and should be easy to follow, understand, maintain and modify. Given the nature of the ASEP/MD method, external programs are needed for the quantum calculations and molecular dynamics simulations. The present version of ASEP/MD includes interface routines for the GAUSSIAN package, HONDO, and MOLDY, but adding support for other programs is straightforward. This article describes the program and its usage.

Electron correlation and solvation effects. II. The description of the vibrational properties of a water molecule in a dielectric given by the application of the polarizable continuum model with inclusion of correlation effects

Abstract The ab initio quantum mechanical version of the polarizable continuum model has recently been improved by introducing electron correlation effects (paper I). In the present paper we continue the analysis of the performances of this method by examining the potential energy surface of H 2 O in vacuo and in a medium (ϵ=78.3), at the SCF, MBP2 and MBP3 levels of the formalism. A short discussion about the relevance of this approach to gain some information about structural features of bulk water is also included.

Solvent effects by means of averaged solvent electrostatic potentials: Coupled method

In this article we propose a mean field theory that permits the calculation of solvent effects in a direct way by combining quantum mechanics and molecular dynamics simulations. Because of the reduced number of necessary quantum calculations, it is possible to get the same level of theory used for molecules in vacuo. The electronic structure of the solute in solution and the solvent structure around it are optimized in a self‐consistent way. The main characteristics of the proposed method are high‐level quantum calculations in the representation of the solute, a detailed description of the solvent structure through molecular dynamics calculation, inclusion of the mutual polarization of the solute and solvent molecules, and an accurate description of the solute–solvent interaction energy. As an application of the model we studied the polarization of quantum mechanically treated water and methanol molecules in the liquid phase.

About the overestimation of the basis set superposition error on interaction energy calculations for van der Waals systems

A procedure to estimate the basis set superposition error is proposed avoiding the overestimation of the counterpoise correction in the van der Waals interactions. Numerical calculations were carried out in the Ne ⋅⋅⋅ Ne complex at the SCF level.