The PYXAID Program for Non-Adiabatic Molecular Dynamics in Condensed Matter Systems.

This work introduces the PYXAID program, developed for non-adiabatic molecular dynamics simulations in condensed matter systems. By applying the classical path approximation to the fewest switches surface hopping approach, we have developed an efficient computational tool that can be applied to study photoinduced dynamics at the ab initio level in systems composed of hundreds of atoms and involving thousands of electronic states. The technique is used to study in detail the ultrafast relaxation of hot electrons in crystalline pentacene. The simulated relaxation occurs on a 500 fs time scale, in excellent agreement with experiment, and is driven by molecular lattice vibrations in the 200-250 cm(-1) frequency range. The PYXAID program is organized as a Python extension module and can be easily combined with other Python-driven modules, enhancing user-friendliness and flexibility of the software. The source code and additional information are available on the Web at the address http://gdriv.es/pyxaid . The program is released under the GNU General Public License.