Multi-reference electron-correlation methods for open-shell molecules:
In the past, we have been involved in development of a variant of multi-reference configuration interaction (MRCI) method using internally contracted configuration basis functions. Its efficiency and applicability for moderate-size inorganic open-shell molecules has been well-established. Current long-term focus in the group is to develop a MRCI method for simultaneous treatment of several excited states and multi-reference coupled-cluster (MRCC) method based on density matrix cumulants. We have been involved in a collaborative work on efficient implementation of a few variants of MRCC methods. We have recently developed a new one-root-at- a-time approach to excited states whose applications are being currently explored.
Non-adiabatic couplings and dynamics:
We have found a novel approach for theory and computations of non-adiabatic couplings using coupled-cluster wave-functions. The approach has been explored for diagonal Born-Oppenheimer correction. Our approach resolves apparent normalization difficulties which existed in the literature. We have explored some applications of ab-initio non-adiabatic dynamics to study photochemistry of small organic molecules. We have also contributed to the development of highly quality potential energy surfaces for nuclear quantum dynamics.
Multiply ionized states of small molecules:
Earlier, we have carried out a study of charge symmetric dissociation of dications of N2 and CO molecule by computing potential energy curves for several states contributing to observed kinetic energy release pattern in electron impact ionization experiments. Recently, we have applied a new procedure to compute high-lying states of molecular nitrogen with one or more core and valence holes.
Magnetic spin-state energy gaps in organic tri-radicals:
Recently, in a collaborative work, we have computationally studied the quartet-doublet energy gaps of several organic tri-radicals based on Blatter’s radical. We have systematically applied multi-reference methods to compute all the states of a spin-multiplet arising from a tri-radical character. Further studies on tetra-radical possibilies are being explored. A new theoretical procedure to compute magnetic exchange couplings for multi-center radicals is also under development.