SPLIT INTEGRATION SYMPLECTIC METHOD FOR MOLECULAR-DYNAMICS INTEGRATION

An explicit Split Integration Symplectic Method (SISM) for molecular d ynamics (MD) simulations is described. This work is an extension of an efficient symplectic integration algorithm introduced by Janezic and Merzel (J. Chem. Inf: Comput. Sci 1995, 35, 321-326). SISM is based on splitting of the total. Hamiltonian of the system into a harmonic par t and the remaining part in such a way that both parts can be efficien tly computed. The Hamilton equations of motion are then solved using t he second order generalized leap-frog integration scheme in which the high-frequency motions are treated analytically by the normal mode ana lysis which is carried out only once, at the beginning of the calculat ion. SISM requires only one force evaluation per integration step; the computation cost per integration step is approximately the same as th at of the standard leap-frog-Verlet (a,FV) method, and it allows an in tegration time step up to an Order of magnitude larger than can be use d by other methods of the same order and complexity. The simulation re sults of selected examples-MD simulations of a model system of linear chain molecules of the form H-(-C=C-)(2)-H and a model system of flexi ble CO2 molecules-show that the SISM posses long term stability and th e ability to use long time steps. The approach for MD simulations desc ribed here is general and applicable to any complex system.