Theoretical Chemistry/Chemical Physics

        The main focus of our present research efforts is the direct, time-dependent simulation of chemical reactions. In that approach, a reaction is simulated in the same way the process evolves in ôreal lifeö (i.e. by evaluating instantaneously the reaction evolution and its acting molecular forces ôon the flyö, without the cumbersome time-independent predetermination of potential energy surfaces). In the main, quantum mechanics is the theoretical framework of our simulations. However, even with the current computer technology, full quantum-mechanics descriptions of large chemical systems remain impractical and recurrences to more feasible classical-mechanics treatments are inevitable. Therefore, we advocate a generalized quantum/classical (Q/C) approach to ab initio molecular mechanics where molecular degrees of freedom and/or molecular regions are distributed into quantum and classical treatments. Degrees of freedom less critical for quantum effects (e.g. nuclear translational, rotational and vibrational motions under some circumstances) and/or a peripheral molecular region not housing quantum processes can be treated via classical mechanics with added quantum corrections.  Conversely, the central region containing quantum phenomena (e.g. tunneling) must be described quantum-mechanically.

 Toward such a goal, we are developing a novel Q/C methodology that permits making transitions from quantum to classical treatments in a gradual and continuous way; we attain such flexibility by exploiting the properties of coherent states (CS). Broadly speaking, CS are sets of quantum states that permit expressing quantum dynamical equations in a classic-like format in terms of generalized positions and momenta. Some CS are also quasi-classical if their generalized positions and momenta obey classical mechanics. A CS-formulated dynamics is still quantum but in a classic-like format as close to classical mechanics as possible; furthermore, if a quasi-classical CS is employed for a molecular region and/or a degree of freedom then a classical dynamics with a quantum state is obtained and a Q/C partition is created.

 A highlight of creativity in our CS efforts is the original formulation of novel types of CS to implement such a CS dynamics. Whereas nearly all previous chemical research on CS has mostly dealt with the celebrated Glauber CS to describe nuclear motions, we are  endeavoring for the creation and/or use of novel types of CS for all types of particles (nuclei and electrons) and for all types of dynamics (translational, rotational, vibrational, electronic)