Conventional molecular dynamics (MD) approaches like Car-Parinello
(CPMD), Born-Oppenheimer (BOMD) or Ehrenfest MD have in common that
the electronic degrees of freedom are always described in terms of
a closed quantum system. By construction, CPMD and BOMD only refer
to the ground-state Born-Oppenheimer surface, whereas Ehrenfest MD
can take into account electronic excitations. However, in all cases
the description in terms of a closed electronic system excludes the
possibility of electronic relaxation and decoherence.
Based on stochastic Kohn-Sham equations, a new MD approach is presented
that allows for an open quantum system description of both the electronic
and the nuclear degrees of freedom.
The new approach is illustrated with a MD study of vibrational and
rotational relaxation in 4-(N,N-dimethylamino)benzonitrile (DMABN).
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