Benjamin G. Levine, Joshua D. Coe, Aaron M. Virshup, Hongli Tao, Christian R. Evenhuis, William J. Glover, Toshifumi Mori, Michal Ben-Nun and Todd J. Martinez.

Bibliography:

B. G. Levine, J. D. Coe, A. M. Virshup and T. J. Martinez, Chem. Phys. 347, 3 (2008).

M. Ben-Nun and T. J. Martinez, Chem. Phys. Lett. 298 57 (1998).

All publications resulting from use of this program must acknowledge the above. See also:

B. G. Levine and T. J. Martinez, J. Phys. Chem. A 113, 12815 (2009).

T. J. Martinez, Acc. Chem. Res. 39, 119 (2006).

The AIMS module implements the Ab Initio Multiple Spawning method to perform dynamics calculations on multiple electronic states. Although the program was designed for non-adiabatic dynamics with CASSCF wavefunctions, it can be used quite generally for first principles molecular dynamics, provided that nuclear gradients are available.

AIMS provides a description of a time-evolving molecular wavepacket with a multi-configurational,
product gaussian function basis. To allow the size of the basis set to remain small while describing
the wavepacket dynamics, the centers of the full-dimensional gaussian functions follow classical
trajectories while their widths are kept fixed (the frozen Gaussian approximation). When these
classical trajectories encounter regions of large non-adiabatic coupling to another electronic state,
new basis functions are *spawned* on the coupled state and the Time Dependent Schrödinger
Equation is solved in order to describe population transfer between the electronic states. In this way,
the description of the wavepacket can be systematically improved by increasing the number of initial
trajectory basis functions, while reducing the coupling threshold at which trajectories spawned.
Alternatively, spawning can be disabled, and the method will reduce to traditional first-principles
classical molecular dynamics when a single trajectory basis function is used.