Input for CP Dynamics

For the CP-MD job you need a new input file, which should be copied into the same directory, where you completed the wavefunction optimization run. Same as for the geometry optimization, we only need to change the &CPMD section of the input file. In fact any change to the other sections (&DFT, &SYSTEM, or &ATOMS may render the wavefunction in the restart file incompatible with the system description and a new wavefunction optimization would be required.

&CPMD
 MOLECULAR DYNAMICS CP
 RESTART WAVEFUNCTION COORDINATES LATEST
 TRAJECTORY XYZ
 ISOLATED MOLECULE
 TEMPERATURE
  50.0D0
 MAXSTEP
  200
 TIMESTEP
  4.0
 EMASS
  400.0
&END

The keyword MOLECULAR DYNAMICS CP defines the job type. Furthermore we tell the CPMD program to pick up the previously calculated wavefunction and coordinates from the latest restart file (which is named RESTART.1 by default, the name of while is read from the file LATEST). MAXSTEP limits the MD trajectory to 200 steps and the equations of motion will be solved for a time step of 4 atomic units ( $\approx 0.1$ femtoseconds). We set the fictitious electron mass (EMASS) to 400a.u. The temperature of the system will be initialized to 50K via the TEMPERATURE keyword (note that this is no thermostatting, this will only assign initial velocities). Please take special note of the ISOLATED MOLECULE. This determines how the temperature of the total system is calculated (bulk systems have no rotational degrees of freedom unlike isolated molecules or clusters. In the case of only two atoms, this difference is large. Just try it out). The keyword TRAJECTORY XYZ will have CPMD write the coordinates additionally to a file TRAJEC.xyz, which can be easily visualized with many popular molecular visualization programs.