Interface of the polarizable continuum model of solvation with semi-empirical methods in the GAMESS program

An interface between semi-empirical methods and the polarized continuum model (PCM) of solvation successfully implemented into GAMESS following the approach by Chudinov et al (Chem. Phys. 1992, 160, 41). The interface includes energy gradients and is parallelized. For large molecules such as ubiquitin a reasonable speedup (up to a factor of six) is observed for up to 16 cores. The SCF convergence is greatly improved by PCM for proteins compared to the gas phase

Speedup by using multiple cores with PCM enabled for single gradient evaluation.

<p>Speedup by using multiple cores with PCM enabled for single gradient evaluation.</p

Predicted electrostatic solvation free energies of oxonium type molecules.

<p>Obtained results using PM3/PCM compared with results by Chudinov <i>et al</i>. (labelled "Ref") and RHF/STO-3G/PCM results. PM3/PCM numbers in parenthesis are deviations to the reference. RHF/STO-3G deviations are taken to PM3/PCM results. All numbers are in kcal mol.</p

Ideal integrals rotated onto the molecular frame.

<p>Ideal integrals rotated onto the molecular frame.</p

Optimization steps and frequencies for solvated molecules.

<p>Number of optimization steps for PM3/PCM and RHF/STO-3G/PCM optimizations along with Mean Absolute Deviations (MADs) of vibrational frequencies when going from gas phase to a solvated molecule for all 20 small molecules tested in this work. All optimizations were done in Cartesian coordinates. Translational and rotational frequencies are not included. Dashes marks unconverged structures after 100 optimization steps.</p><p>marks optimized structures with at least one imaginary frequency.</p

Absolute timings for energy and gradient evaluations.

<p>Absolute timings in seconds for energy and gradient evaluation for various proteins using both gas phase PM3 and PM3/PCM. Numbers in parenthesis are analytic electronic field gradient timings used in the analytical PM3/PCM gradient. No gas phase SCF converged without DIIS.</p