Example (GAMESSUS): Dynamics of H2+ Fewest Switches Surface Hopping.

This is an example of a fewest-switches-surface-hopping calculation for an ionized hydrogen molecule (H2+). See the directory:

Examples/xpyder/h2+/

Preparation

  1. set your environment variable CDTK_GAMESSUS to the path of the gamessus directory. For example:

    export CDTK_GAMESSUS=$HOME/gamess/

    Instead of ‘$HOME/gamess/’ insert the actual path of your gamess installation.

  2. Depending on your gamess installation, output is written to the scratch file folder. This is configured in the rungms script in your gamess installation. Edit the script rungms accordingly so that the output is written in the current working directory. You may want to comment out the lines set SCR=~/gamess/restart and #set USERSCR=~/gamess/restart, instead, set the SCR and USERSCR environment variables to .. For example:

    export SCR=.
export USERSCR=.

    Note that the local directory in which the simulation is run should be a rapidly accessible disk (i.e., a local folder or ramdisk) - otherwise there will be huge performance losses.

Running

To run the example, execute:

xpyder -i input_h2+_dynamics_no_field -d H2+_dynamics_no_field

Details of the Inputfile

The file input_h2+_dynamics_no_field is the input file used for the calculation:

$SYSTEM
  qchemistry  = gamess
  xunit       = an
  rseed       = 1
  keepinp
  keeplog
$END

$gamess
  memddi = 2
  mwords = 2
  gbasis = TZV
  icharg = 1
  mult = 2
  ncore = 0
  nact = 2
  nels = 1
  wstate = 1.0,1.0
  nstate = 2
  sz = 0.5
  mxxpan = 100
  fullnr = .true.
$end

$trajectory
  dt =  0.01   fs
  tf =  6.0   fs
$end

$quantum
  type      = fssh
  rescaling = nac
  istate    = 1
  nstates   = 2
  first_step = 1.0
$end

$cartPOS
  H    0.0   0.0   -0.5292344732
  H    0.0   0.0    0.5292344732
$end

$cartVEL
  H  0.0  0.0    0.00
  H  0.0  0.0   -0.00
$end

  1. $SYSTEM

    • qchemistry = gamess specifies the quantum chemistry tool.

    • xunit = an specifies the unit in the coordinates of the atom is specified. “an” refers to Angstrom

    • rseed = 1 gives the initial seed value for the random number generator used for the calculations.

    • keepinp and keeplog will keep the input and the outputput files of the quatum chemistry tool. (If you do not give this option, then it will remove the files)

  2. $gamess

    • this gives the input detials such as the basis used, active space etc., for the electronic structure calculation.

  3. $trajectory - “dt” is for the time step used for the calculation (in fs). - “tf” is the final time ie., the time till the calculation will last (in fs).

  4. cartPOS and cartVEL - this gives the intial position and velicity of the atoms.

  5. quantum

    • type = fssh specifies the type of surface hopping. “fssh” denotes Tully’s Fewest Switches Surface hoping. (one can give “nohop” to avoid the surface hopping dynamics).

    • istate and nstate gives the initial state at which the trajectory present and no. of states respectively.

    • rescaling specifies the type of rescaling when a hop is performed. The parameter nac specifies rescaling based on non-adiabatic coupling vectors, commonly used for surface hopping. Alternatively, one can give grd for rescaling based on the gradiant.

Output data

The folder H2+_dynamics_no_field contains all the output files.

  1. P.log gives the population of the states by solving the time dependent Schroedinger equation.

  2. C.log gives the co-efficients for the electronic states.

  3. V_ad.log gives the adiabatic potential energies for all the states.

  4. R.log gives the position of the atoms at the end of the calculation.

  5. V.log gives the velocity of the atoms.

  6. S.log gives the active surface of the trajectory.

  7. NAC.log gives the coupling terms, i.e., the off diagonal terms of the Hamiltonian.

  8. E.log gives the potential energy, kinetic energy and totol energy of the trajectory.

  9. Switch.log gives the details of the hopping, its probability, the random number used and also the reason for the hopping.

Note: apart from all the above files, there will be output and input files of the eletronic structure calculations based on the input option.