Steven W. Rick

Learn More
A new molecular dynamics model in which the point charges on atomic sites are allowed to fluctuate in response to the environment is developed and applied to water. The idea for treating charges as variables is based on the concept of electronegativity equalization according to which: (a) the electronegativity of an atomic site is dependent on the atom's(More)
Theories of solvation free energies often involve electrostatic potentials at the position of a solute charge. Simulation calculations that apply cutoffs and periodic boundary conditions based on molecular centers result in center-dependent contributions to electrostatic energies due to a systematic sorting of charges in radial shells. This sorting of(More)
Molecular dynamics simulations are used to calculate the free energy of methane association in water, using the polarizable fluctuating charge model that treats the charges on atomic sites as dynamical variables. Compared with previous studies using nonpolarizable potentials, the inclusion of polarizability leads only to small differences in the methane(More)
We explore and discuss several important issues concerning the derivation of many-body force fields from ab initio quantum chemical data. In particular, we seek a general methodology for constructing ab initio force fields that are ''chemically accurate'' and are computationally efficient for large-scale molecular dynamics simulations. We investigate two(More)
Computer simulations of ice Ih with different proton orientations are presented. Simulations of proton disordered ice are carried out using a Monte Carlo method which samples over proton degree of freedom, allowing for the calculation of the dielectric constant and for the examination of the degree of proton disorder. Simulations are also presented for two(More)
Calculation of single-ion free energies of solvation 1 requires careful treatment of electrostatic interactions. In computer simulations of ion solvation, only a finite number of solvent molecules are considered. To mimic an infinite system, periodic boundary conditions are generally employed. Ewald summation provides a consistent means to calculate(More)
Replica exchange is a powerful simulation method in which simulations are run at a series of temperatures, with the highest temperature chosen so phase space can be sampled efficiently. In order for swaps to be accepted, the energy distributions of adjacent replicas must have some overlap. This can create the need for many replicas for large systems. In(More)
A new method for performing molecular dynamics simulations with fluctuating charge polarizable potentials is introduced. In fluctuating charge models, polarizability is treated by allowing the partial charges to be variables, with values that are coupled to charges on the same molecule as well as those on other molecules. The charges can be efficiently(More)
The transfer of small amounts of charge between neighboring particles can be a significant part of interactions among particles. A model is developed for treating charge transfer (CT) combined with the Drude model for polarizability to create an efficient model for liquid water which includes both CT and polarizability. The model is shown to be accurate for(More)
Computational studies are presented examining the degree of proton disorder in argon and molecular hydrogen sII clathrate hydrates. Results are presented using a variety of model potentials for the dielectric constant, the proton order parameter, and the molecular volume for the clathrate systems. The dielectric constant for the clathrate systems is found(More)
  • 1