Generalization of the Gaussian Electrostatic Model: A molecular density based force field

COMP 64

G. Andres Cisneros, cisnero1@niehs.nih.gov1, Jean-Philip Piquemal, jpp@lct.jussieu.fr2, and Thomas A. Darden1. (1) Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Box 12233, MD F0-08, Research Triangle Park, NC 27709, (2) Laboratoire de Chimie Théorique, Université Pierre et Marie Curie (Paris VI), UMR 7616 du CNRS, Case Courrier 137, 4, place Jussieu, 75252 Paris cedex 05, Paris, France
We have recently introduced a force field that relies on the reproduction of molecular electronic densities by means of density fitting methods to calculate intermolecular interactions, the Gaussian electrostatic model (GEM). In the initial implementation (GEM-0), the auxiliary basis sets (ABS) used for the fit included only s-type Gaussian functions. GEM-0 employs the fitted electronic densities to reproduce each contribution of the Constrained Space Orbital Variation (CSOV) energy decomposition scheme. Here we present an extension of GEM-0 to higher order angular momentum ABSs. In all cases the intermolecular interaction energies are calculated by means of Hermite Gaussian functions using a generalized McMurchie-Davidson recursion for all the required integrals. The use of Hermite Gaussians also provides a straightforward point multipole decomposition. A reference molecular frame (local frame) formalism is employed for the rotation of the fitted expansion coefficients. Additionally, reciprocal space based methods which include the Particle Mesh Ewald (PME) and Fast Fourier Poisson (FFP) methods have been implemented to improve computational speed. Coulomb and exchange-repulsion intermolecular interaction results for ten water dimers, and one-dimensional surface scans for the canonical water dimer, a formamide and a stacked benzene dimers are presented for B3LYP/6-31G* and B3LYP/aug-cc-pVTZ densities, fitted with three different ABSs. All results are in reasonable agreement with CSOV, around 0.1 kcal/mol and 0.15 kcal/mol error for Coulomb and exchange respectively. Timing results for single Coulomb energy-force calculations for (H2O)n n= 64, 128, 256, 512 and 1024 in periodic boundary conditions with PME and FFP at two different RMS force tolerances are also presented. Furthermore, results from an initial QM/MM implementation for electrostatic embedding using GEM are also shown and compared to conventional point charge QM/MM results. These show that point charges significantly under-polarize the QM part at hydrogen bonding distances, while GEM provides the correct polarization response.
 

Emerging Technologies
1:00 PM-5:00 PM, Sunday, August 19, 2007 BCEC -- 156B, Oral

Division of Computers in Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007