A b initio quantum direct dynamics simulations of ultrafast photochemistry with Multiconfigurational Ehrenfest approach

Zombie states for description of structure and dynamics of multi-electron systems

“…where ζ Thus, introduction of Zombie States, which can be viewed as antisymmetrised Coherent States of a set of two-level systems, and the form of second quantization electronic structure Hamiltonian given by (11) and (13) on the manifold of Zombie States (2) is the first result of this paper. In Sec.…”

“…In Appendix A, the sign-changing rule (12) of the operators (11) is derived, starting from standard definition of creation and annihilation operators. 6,7 Here, we will only mention that the sign-changing rule in (11) originates from the fact that in the usual second quantization approach, 6 operating within the manifold of N-electron Slater determinants with no unoccupied spin-orbitals included, creation and annihilation operators act on the first column of the Slater determinant. As a result, when acting withb + m orb m , the m-th column must be moved to or from the first position, which is also equivalent to changing sign of all other occupied spin-orbitals on the left from m.…”

“…They also were in perfect agreement with those obtained by MOL-PRO Full CI and by diagonalization of the Hamiltonian (13) in the basis (6). Therefore, using simple sign-changing rule (11) in the definition of creation and annihilation operators is exact and ZSs with the sign-changing rule (11) can be used as a basis set for numerical calculations instead of Fock Space functions (6) or Fermionic CSs with Grassmann algebras. 1 After finding eigen values E n and eigen vectors φ n in Full Fock Space electronic propagator written as…”

“…Several Canonical Gaussian Coherent States-based methods have been developed and proved to be valuable techniques of atomistic simulations. They have been used extensively to model the dynamics of nuclei in molecules for chemical reaction dynamics, 10,11 in simulations of the dynamics of electrons in strong laser field, 12 in simulations of quantum decoherence, 13 etc. An important feature of the Canonical CS-based methods, which makes them particularly efficient, is that the basis CSs is time-dependent.…”

“…Electrons are treated in adiabatic basis. 10,11 Calculating adiabatic potential energy surfaces and nonadiabatic coupling matrix elements (NACME) with the help of Electronic structure theory is the most computationally expensive part. Treating electronic part with Zombie States would require only cheap Hartree-Fock electronic structure.…”