This keyword specifies the initial nuclear velocities and, therefore, the
initial temperature of a BOMD simulation.
RANDOM / ZERO / READ
RANDOM || Random velocities from a uniform distribution. |
ZERO || Initial velocities are set to zero. |
READ || Initial velocities are read from the input file. |
P=0 || Adjust the initial velocities to zero linear momentum. |
LP=0 || Adjust the initial velocities to zero linear and
angular momentum. |
T=Real || Specifies the temperature [K] to which the initial
velocities are scaled. Default is 300 K.|
The positions and velocities of the nuclei must be initialized at the beginning
of a BOMD simulation. Although the nuclear positions are defined by the GEOMETRY
keyword (see 4.1.1), the nuclear velocities are initialized by the
VELOCITIES keyword. By default, random velocities are assigned to the nuclei. Under
the option ZERO, the nuclei are frozen at the beginning of the BOMD simulation.
The nuclear velocities can also be read from the input file deMon.inp by use
of the read option of the VELOCITIES keyword. The individual atomic velocities are then
read from the keyword body of the VELOCITIES keyword. The syntax and hierarchy
of these assignments is similar to those for basis set assignment (see 4.3.1).
Thus, initial nuclear velocities can be assigned to individual atoms by the atomic
symbol (e.g. H4) or to atom groups by the element symbol (e.g. H).
The following example assigns nuclear velocities to the atoms in a water molecule:
O 0.00 0.00 0.00
H1 0.10 0.05 0.00
H2 0.20 -0.07 0.00
Depending upon the unit definition (Å or Bohr) in the GEOMETRY keyword (see
4.1.1), the velocity unit is either Å/fs or Bohr/fs. The READ option
can be combined with the RANDOM or ZERO option which then acts only on the atom
velocities that are not explicitly defined in the keyword body of VELOCITIES.
The options P=0 and LP=0 of the VELOCITIES keyword are used to adjust the initial
velocities to zero linear or zero total linear and angular momentum. Please note
that these options will modify the read-in velocities. The temperature of the
initial nuclear velocities can be specified according to the equipartition theorem
via the option T.