Energetics and structure in solvent: A dielectric continuum model of solvation combined with molecular mechanics, Ab Initio, and Semi-empirical molecular orbital treatments of the solute

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:447549

Tawa, G J ^[1]; Pratt, L R; Martin, R L ^[2]

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1. Frederick Cancer Research and Development Center, MD (United States)
2. Los Alamos National Lab., NM (United States)

We present a method for computing the electrostatic component of the solvation free energy, {Delta}G{sup el}, of a solute molecule in the presence of solvent modeled as a dielectric continuum. The method is based on an integral form of Poisson`s equation which is solved to obtain a distribution of induced polarization charge at the solute-solvent dielectric interface. The solution of Poisson`s equation is obtained by application of a boundary element procedure. The method is tested by comparing its predictions of {Delta}G{sup el} to exact values for several model problems. The method is then used in a variety of contexts to assess its qualitative prediction ability. It is first combined with a molecular mechanics treatment of the solute to evaluate the effects of aqueous solvent on the conformational equilibria of several small molecules of interest-these are N-methyl acetamide and alanine dipeptide. For both molecules dielectric continuum solvation predicts torsional free energies of solvation that are in accord with other more complete treatments of solvation. The method is then combined with ab initio and semi-empirical molecular orbital theory for the solute. Self consistent reaction field calculations (SCRF) are performed to evaluate the correlation is in general very good. Relative agreement with experiment is best for ions where electrostatics predominate and worst for non-polar neutral molecules were electrostatics are minor. Semi-empirical configuration interaction SCRF calculations are also performed in the presence of solvent in order to determine ground-to-excited state absorption energy shifts for formaldehyde and indole mine ground-to-excited state absorption energy shifts for formaldehyde and indole when placed in water. We find a rough correlation between transition energy shifts and the dipole moments of the initial and final states involved in the transition.

• OSTI ID: 447549
• Report Number(s): CONF-960343--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
66 PHYSICS
CALCULATION METHODS
ELECTRONIC STRUCTURE
FREE ENERGY
MOLECULAR STRUCTURE
POISSON EQUATION
SOLVENTS