Keyword VELOCITIES

This keyword specifies the initial nuclear velocities and, therefore, the initial temperature of a BOMD simulation.
Options:
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.

Description:
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:

 VELOCITIES READ
 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.