Ab initio molecular-dynamics techniques extended to large-length-scale systems

The Born-Oppenheimer approximation divides the problem of quantum molecular dynamics into two familiar problems: (1) solution for the electronic wave functions for a given instantaneous arrangement of ions and (2) the motion of the atomic cores under the influence of those wave functions. A combination of conjugate-gradient methods to solve (1) with standard molecular dynamics to solve (2) results in a scheme that is at least two orders of magnitude more accurate than previously possible, thus allowing accurate calculation of dynamic correlation functions while maintaining tolerable energy conservation for microcanonical averages of those correlation functions over picosecond time scales. By employing conjugate-gradient techniques, this method is used to extend the applicability of finite-temperature ab initio techniques to systems with large length scales.