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Relativistic Internally Contracted Multireference Electron Correlation Methods
We report internally contracted relativistic multireference configuration
interaction (ic-MRCI), complete active space second-order perturbation
(CASPT2), and strongly contracted n-electron valence state perturbation theory
(NEVPT2) on the basis of the four-component Dirac Hamiltonian, enabling
accurate simulations of relativistic, quasi-degenerate electronic structure of
molecules containing transition-metal and heavy elements. Our derivation and
implementation of ic-MRCI and CASPT2 are based on an automatic code generator
that translates second-quantized ansatze to tensor-based equations, and to
efficient computer code. NEVPT2 is derived and implemented manually. The
rovibrational transition energies and absorption spectra of HI and TlH are
presented to demonstrate the accuracy of these methods
On-the-fly CASPT2 surface hopping dynamics
We report the development of programs for on-the-fly surface hopping dynamics
simulations in the gas and condensed phases on the potential energy surfaces
computed by multistate multireference perturbation theory (XMS-CASPT2) with
full internal contraction. On-the-fly nonadiabatic dynamics simulations are
made possible by improving the algorithm for XMS-CASPT2 nuclear energy gradient
and derivative coupling evaluation. The program is interfaced to a surface
hopping dynamics program, Newton-X, and a classical molecular dynamics package,
tinker, to realize such simulations. On-the-fly XMS-CASPT2 surface-hopping
dynamics simulations of 9H-adenine and an anionic GFP model chromophore
(para-hydroxybenzilideneimidazolin-5-one) in water are presented to demonstrate
the applicability of our program to sizable systems. Our program is implemented
in the bagel package, which is publicly available under the GNU General Public
License
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