Strong field ionization of many electron systems: A quantum chemical challenge

A non-variational Time-Dependent Multiconfiguration Self-Consistent Field (TDMCSCF) scheme has been developed [Nguyen-Dang T.T., Peters M., Wang S.-M., Sinelnikov E., and Dion F., J. Chem. Phys. 127, 174107 (2007)] to describe, by an ab-initio approach, the time-resolved electron dynamics of a laser-driven many-electron atomic or molecular system. As an L ² method, this approach faces severe challenges when ionization and large-amplitude electronic motions are addressed. We present here an extension of this TDMCSCF scheme to include multiple ionization processes, using a Feschbach state-partitioning formalism, allowing the bound electrons’ dynamics to be treated by the L ²-TDMCSCF method, while the ionized electrons can be treated separately by an alternative approach. We present results of proof-of-principle calculations pertaining to the single and double ionizations of H ₂ and discuss methodological issues such as the systematic corrections that could be brought, using this approach, to the strong field approximation (SFA).     

Nonvariational time-dependent multiconfiguration self-consistent field equations for electronic dynamics in laser-driven molecules

A time-dependent multiconfiguration self-consistent field (TDMCSCF) scheme is developed to describe the time-resolved electron dynamics of a laser-driven many-electron atomic or molecular system, starting directly from the time-dependent Schrodinger equation for the system. This nonvariational formulation aims at the full exploitations of concepts, tools, and facilities of existing, well-developed quantum chemical MCSCF codes. The theory uses, in particular, a unitary representation of time-dependent configuration mixings and orbital transformations. Within a short-time, or adiabatic approximation, the TDMCSCF scheme amounts to a second-order split-operator algorithm involving generically the two noncommuting one-electron and two-electron parts of the time-dependent electronic Hamiltonian. We implement the scheme to calculate the laser-induced dynamics of the two-electron H2 molecule described within a minimal basis, and show how electron correlation is affected by the interaction of the molecule with a strong laser field.     

Some properties of the Lagrange multiplier μ in density functional theory

Some new properties of the Lagrange multiplier μ introduced through the normalization constraint on ρ in the variations of energy density functionals are determined. Through arguments concerning the homogeneity properties of these functionals with respect to μ, it is demonstrated that at the point of variation μ = μ₀ = E₀/N, where E₀ is the ground state energy and N is the total particle number. It is also shown that the value of μ₀ is independent of the normalization imposed on ρ. The interpretation of μ₀ as a chemical potential is discussed in the light of these findings.