MOLECULAR-DYNAMICS SIMULATIONS OF PROTEINS IN WATER WITHOUT THE TRUNCATION OF LONG-RANGE COULOMB INTERACTIONS

A new program package (COSMOS90) for molecular dynamics simulations was developed to simulate large molecular systems consisting of more than tens of thousands of atoms without the truncation of long-range coulomb interactions. This program package was based on a new approximation scheme (PPPC) for calculating efficiently the coulomb interactions without sacrificing accuracy. In this approximation scheme, the group of charges at a long distance from each atom was represented by a total charge and total dipole moment of the group. In order to assess the accuracy of PPPC and the ability of COSMOS90, molecular dynamics simulations were carried out for a large system consisting of 16108 atoms (human lysozyme in water) for 50 ps using this program package. The coulomb energy per solute atom was calculated with only five percent of the error found in the 10 angstrom cut-off approximation (about 0.9 kcal/mol versus 18 kcal/mol, respectively). The molecular dynamics simulations using COSMOS90 require no more CPU time than the simulations based on the 10 angstrom cut-off approximation of the conventional programs for macromolecular simulations.