  Nonadiabatic molecular dynamics occur in a wide range of chemical reactions
and femtochemistry experiments involving electronically excited states. These
dynamics are hard to treat numerically as the system's complexity increases and
it is thus desirable to have accurate yet affordable methods for their
simulation. Here, we introduce a linearized semiclassical method, the
generalized discrete truncated Wigner approximation (GDTWA), which is
well-established in the context of quantum spin lattice systems, into the arena
of chemical nonadiabatic systems. In contrast to traditional continuous mapping
approaches, e.g. the Meyer-Miller-Stock-Thoss and the spin mappings, GDTWA
samples the electron degrees of freedom in a discrete phase space, and thus
forbids an unphysical unbounded growth of electronic state populations. The
discrete sampling also accounts for an effective reduced but non-vanishing
zero-point energy without an explicit parameter, which makes it possible to
treat the identity operator and other operators on an equal footing. As
numerical benchmarks on two Linear Vibronic Coupling models show, GDTWA has a
satisfactory accuracy in a wide parameter regime, independently of whether the
dynamics is dominated by relaxation or by coherent interactions. Our results
suggest that the method can be very adequate to treat challenging nonadiabatic
dynamics problems in chemistry and related fields.
