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Ab initio molecular dynamics: Propagating the density matrix with gaussian orbitals. IV. Formal analysis of the deviations from born‐oppenheimer dynamics
Author(s) -
Iyengar Srinivasan S.,
Schlegel H. Bernhard,
Voth Gregory A.,
Millam John M.,
Scuseria Gustavo E.,
Frisch Michael J.
Publication year - 2003
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1560/glw2-8nvq-4n6t-6c92
Subject(s) - chemistry , born–oppenheimer approximation , molecular dynamics , commutator , gaussian , ab initio , density matrix , context (archaeology) , ab initio quantum chemistry methods , matrix (chemical analysis) , statistical physics , computational chemistry , quantum mechanics , classical mechanics , physics , molecule , paleontology , lie conformal algebra , organic chemistry , lie algebra , quantum , biology , chromatography
In the context of the recently developed Atom‐centered Density Matrix Propagation (ADMP) approach to ab initio molecular dynamics, a formal analysis of the deviations from the Born—Oppenheimer surface is conducted. These deviations depend on the fictitious mass and on the magnitude of the commutator of the Fock and density matrices. These quantities are found to be closely interrelated and the choice of the fictitious mass provides a lower bound on the deviations from the Born—Oppenheimer surface. The relations are illustrated with an example calculation for the Cl − (H 2 O) 25 cluster. We also show that there exists a direct one‐to‐one correspondence between approximate Born—Oppenheimer dynamics, where SCF convergence is restricted by a chosen threshold value for the commutator of the Fock and density matrices, and extended Lagrangian dynamics performed using a finite value for the fictitious mass. The analysis is extended to the nuclear forces used in the ADMP approximation. The forces are shown to be more general than those standardly used in Born—Oppenheimer dynamics, with the addition terms in the nuclear forces depending on the commutator mentioned above.