Jacopo Tomasi

Electrostatic interaction of a solute with a continuum. A direct utilizaion of AB initio molecular potentials for the prevision of solvent effects

Abstract A method is presented which utilizes the calculation of the molecular electrostatic potential or the electric field at a discrete number of preselected points to evaluate the environmental effects of a solvent on the properties of a molecular system. No limitations are imposed on the composition and dimension of the solute, on the goodness of the corresponding wavefunction, or on the shape of the cavity in the dielectric. Several levels of approximation, which evidence the effect of self-polarization of the system of surface charges, the influence of the tails of the solute charge distribution going beyond the limits of the cavity, and the effect of the polarization of the solute, are examined and discussed.

A new integral equation formalism for the polarizable continuum model: Theoretical background and applications to isotropic and anisotropic dielectrics

We present a new integral equation formulation of the polarizable continuum model (PCM) which allows one to treat in a single approach dielectrics of different nature: standard isotropic liquids, intrinsically anisotropic medialike liquid crystals and solid matrices, or ionic solutions. The present work shows that integral equation methods may be used with success also for the latter cases, which are usually studied with three-dimensional methods, by far less competitive in terms of computational effort. We present the theoretical bases which underlie the method and some numerical tests which show both a complete equivalence with standard PCM versions for isotropic solvents, and a good efficiency for calculations with anisotropic dielectrics.

Ab initio study of solvated molecules: a new implementation of the polarizable continuum model

Abstract We have implemented an efficient version of the polarizable continuum solvation model in the GAUSSIAN94 package. This version exploits a new definition of surface elements area, and a direct formulation of the electrostatic self-consistent problem. Non-electrostatic contributions to the molecular free-energy in solution are calculated in the same framework. Several possible definitions of the molecular cavity are examined, and the results compared to those of other continuum solvation methods already available in GAUSSIAN94.

Continuum solvation models: A new approach to the problem of solute’s charge distribution and cavity boundaries

In continuum solvation models the definition of a cavity that embeds the solute molecule leads to problems related to the portion of solute’s electronic charge lying outside its boundaries (charge tails). The correction strategies developed so far can be shown to work insufficiently, since they only correct the global charge defect, but lead to considerable local errors. The present paper will be focused on the theoretical and technical aspects of this problem, and it will present in detail a new method which allows a very refined treatment of solute’s charge tails in the outer space; some numerical results of solutes in water will be shown and discussed. As further analyses, the introduction of Pauli repulsion term will be considered, and the implications all these effects have on molecular properties, such as (hyper)polarizabilities, numerically evaluated. The new approach has been implemented within the framework of the polarizable continuum model (PCM).

Approximate evaluations of the electrostatic free energy and internal energy changes in solution processes

Abstract A recently proposed procedure for introducing solvent effects in the molecular hamiltonian of a solute is here re-elaborated to get approximate solutions of the corresponding classical electrostatic problem. The basic feature of the original procedure, i.e. the direct utilization of a quantum-mechanical ab initio description of the solute charge distribution in the “continuum” solution model, with cavities of arbitrary shape, is maintained. The meaning of supplementary assumptions introduced in classical calculation 0is discussed, and a comparison is made with analogous evaluations obtained with other approaches

A new definition of cavities for the computation of solvation free energies by the polarizable continuum model

A set of rules for determining the atomic radii of spheres used to build the molecular cavities in continuum solvation models are presented. The procedure is applied to compute the hydration free energy for molecules containing H, C, N, O, F, P, S, Cl, Br, and I at a computational level (Hartree–Fock with a medium size basis set) allowing the study of relatively large systems. The optimized radii reduce the mean error with respect to the experimental solvation energies below 0.20 kcal/mol for a set of 43 neutral solutes and around 1 kcal/mol for 27 ions. Moreover the correct trends are observed for the solvation energies of homolog series, like the series ammonia–trimethylamine, that are not correctly reproduced by usual solvation models.

The IEF version of the PCM solvation method: an overview of a new method addressed to study molecular solutes at the QM ab initio level

Abstract The integral equation formalism (IEF) is a recent method (the grounds have been elaborated at the beginning of 1997) addressed to solve the electrostatic solvation problem at the QM level with the aid of apparent surface charges (ASC). IEF uses a new formalism of this problem, based on integral operators never used before in the chemical community and it manages to treat on the same footing linear isotropic solvent models, as well as anisotropic liquid crystals and ionic solutions. In this overview we emphasize the good performances of IEF at the lowest level of its potentialities, i.e. for isotropic solvents, as a new approach to compute solvation free energies and properties (dipole hyperpolarizabilities) of molecular solutes, as well as energy gradients for geometry optimization procedures. Finally we present a new IEF implementation of the nonequilibrium problem for electronic spectra which appears to be decidedly competitive with the previous more standard ASC formulations.

Geometry optimization of molecular structures in solution by the polarizable continuum model

A new implementation of analytical gradients for the polarizable continuum model is presented, which allows Hartree‐Fock and density functional calculations taking into account both electrostatic and nonelectrostatic contributions to energies and gradients for closed and open shell systems. Simplified procedures neglecting the derivatives of the cavity surface and/or using single spheres for XHn groups have also been implemented and tested. The solvent‐induced geometry relaxation has been studied for a number of representative systems in order to test the efficiency of the procedure and to investigate the role of different contributions. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 404–417, 1998

Ab initio study of ionic solutions by a polarizable continuum dielectric model

Abstract A new implementation of a recently developed formalism to describe chemical systems in ionic solutions is presented. It allows ab initio calculations at the Hartree–Fock and density functional levels on closed and open shell systems, taking into account the ionic atmosphere effects at not too large concentrations. Test calculations on simple systems are compared to experimental data and to values obtained by numerical integration of the Poisson–Boltzmann equation. A more complex system, namely the glycine radical in aqueous solution, is also analyzed.

Geometries and properties of excited states in the gas phase and in solution: Theory and application of a time-dependent density functional theory polarizable continuum model

In this paper we present the theory and implementation of analytic derivatives of time-dependent density functional theory (TDDFT) excited states energies, both in vacuo and including solvent effects by means of the polarizable continuum model. The method is applied to two case studies: p-nitroaniline and 4-(dimethyl)aminobenzonitrile. For both molecules PCM-TDDFT is shown to be successful in supporting the analysis of experimental data with useful insights for a better understanding of photophysical and photochemical pathways in solution.