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#

Molecular Dynamics Calculations

*Ab initio* molecular dynamics (MD) can be carried out on the
ground state Born-Oppenheimer potential hypersurface. At the start
of an MD run the user must specify the initial atomic positions and
velocities and give some general instructions for the run. This is
managed by running the interactive program `Mdprep` and
generating the command file `mdmaster`. If this is
successful, the MD run itself may be started: `jobex -md`

.
Time is then advanced in steps. The electronic potential
energy and its gradients are calculated quantum mechanically at the
required coordinates each timestep (as detailed above, e.g. `dscf`
and `grad`). The MD program `frog` uses the Leapfrog Verlet
algorithm [40] to turn the
gradients into new atomic positions and velocities. The atoms thus
undergo classical Newtonian dynamics on the *ab initio*
potential hypersurface. Trajectory information is recorded in a log
file (`mdlog`). It is possible to instruct `frog` to heat
or cool the system, use a thermostat for canonical dynamics,
conserve total energy or read in new positions or
velocities: the appropriate keywords are described in
Section 15.2.18 below.

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** Up:** Calculation of Molecular Structure
** Previous:** The UFF implementation
** Contents**
** Index**
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