Quantum wavepacket ab initio molecular dynamics: Generalizations using an extended Lagrangian treatment of diabatic states coupled through multireference electronic structure
- Department of Chemistry and Department of Physics, Indiana University, 800 E. Kirkwood Ave, Bloomington, Indiana 47405 (United States)
We present a generalization to our previously developed quantum wavepacket ab initio molecular dynamics (QWAIMD) method by using multiple diabatic electronic reduced single particle density matrices, propagated within an extended Lagrangian paradigm. The Slater determinantal wavefunctions associated with the density matrices utilized may be orthogonal or nonorthogonal with respect to each other. This generalization directly results from an analysis of the variance in electronic structure with quantum nuclear degrees of freedom. The diabatic electronic states are treated here as classical parametric variables and propagated simultaneously along with the quantum wavepacket and classical nuclei. Each electronic density matrix is constrained to be N-representable. Consequently two sets of new methods are derived: extended Lagrangian-QWAIMD (xLag-QWAIMD) and diabatic extended Lagrangian-QWAIMD (DxLag-QWAIMD). In both cases, the instantaneous potential energy surface for the quantum nuclear degrees of freedom is constructed from the diabatic states using an on-the-fly nonorthogonal multireference formalism. By introducing generalized grid-based electronic basis functions, we eliminate the basis set dependence on the quantum nucleus. Subsequent reuse of the two-electron integrals during the on-the-fly potential energy surface computation stage yields a substantial reduction in computational costs. Specifically, both xLag-QWAIMD and DxLag-QWAIMD turn out to be about two orders of magnitude faster than our previously developed time-dependent deterministic sampling implementation of QWAIMD. Energy conservation properties, accuracy of the associated potential surfaces, and vibrational properties are analyzed for a family of hydrogen bonded systems.
- OSTI ID:
- 21559947
- Journal Information:
- Journal of Chemical Physics, Vol. 133, Issue 18; Other Information: DOI: 10.1063/1.3504167; (c) 2010 American Institute of Physics; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACCURACY
DEGREES OF FREEDOM
DENSITY MATRIX
ELECTRONIC STRUCTURE
ELECTRONS
ENERGY CONSERVATION
HYDROGEN
LAGRANGIAN FUNCTION
MOLECULAR DYNAMICS METHOD
NUCLEI
PARTICLES
POTENTIAL ENERGY
SAMPLING
SURFACES
TIME DEPENDENCE
VIBRATIONAL STATES
WAVE FUNCTIONS
WAVE PACKETS
YIELDS
CALCULATION METHODS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY
ENERGY LEVELS
EXCITED STATES
FERMIONS
FUNCTIONS
LEPTONS
MATRICES
NONMETALS