Extended Lagrangian free energy molecular dynamics

Abstract

Extended free energy Lagrangians are proposed for first principles molecular dynamics simulations at finite electronic temperatures for plane-wave pseudopotential and local orbital density matrix-based calculations. Thanks to the extended Lagrangian description, the electronic degrees of freedom can be integrated by stable geometric schemes that conserve the free energy. For the local orbital representations both the nuclear and electronic forces have simple and numerically efficient expressions that are well suited for reduced complexity calculations. A rapidly converging recursive Fermi operator expansion method that does not require the calculation of eigenvalues and eigen-functions for the construction of the fractionally occupied density matrix is discussed. An efficient expression for the Pulay force that is valid also for density matrices with fractional occupation occurring at finite electronic temperatures is also demonstrated.Funding Agencies|US-DoE|DE-AC52-06NA25396|(U.S.) Department of Energy through the LANL LDRD/ER||Swedish Foundation for Strategic Research (SSF) via Strategic Materials Research Center on Materials Science for Nanoscale Surface Engineering|MS2E|Gran Gustafsson Foundation for Research in Natural Sciences and Medicine||T-Division Ten-Bar Java Group|