Example (XMOLECULE): H₂O⁺ hole dynamics

This examples propagates an ionized water molecule using the xmolecule electronic structure toolkit. The dynamics is modelled using fewest switches surface hopping and the electronic structure is calculated using Koopanns’ theorem.

See:

Examples/xpyder/h2o+_xmol/

Preparation

Make sure you have installed XMOLECULE.

Details of the Inputfile input_hole_gto

The file input_hole_gto is the input file used for the calculation:

$SYSTEM
   qchemistry = xmolecule
   xunit = bohr
$END

$xmolecule
   gto = 6-31G_star_star
   HF = yes
   occ = 22221
   gs_occ = yes
$end

$trajectory
   dt = 0.1   fs
   tf = 80.0   fs
$end

$quantum
   type = fssh
   nstates = 4
   istate  = 2
   rescaling = nac
   N = 1
$end


$cartPOS
   O  -0.000000    -0.000000     0.116743
   H  -0.000000    -1.498103     1.300
   H  -0.000000     1.498103     1.200
$end

$cartVEL
   O     0.000000     0.000000     0.000000
   H     0.000000     0.000000     0.000000
   H     0.000000     0.000000     0.000000
$end

$SYSTEM
- qchemistry = xmolecule indicates that xmolecule is used for quantum chemistry engine.

$xmolecule
- gto = 6-31G_star_star specifies the Gaussian basis set.
- HF = yes do Hartree-Fock calculations
- occ = 22221 consider ionized configurations
- gs_occ = yes employ Koopmanns’ theorem

$trajectory
- “dt” is the time step used for the calculation (in fs).
- “tf” is the time of the last time step (in fs).
quantum
- type = fssh employ fewest switches surface hopping
- nstates = 4 number of states. MUST match the number of valence orbitals
- istate = 2 index of starting state: this means that the hole is initially in HOMO-2
- rescaling = nac do rescaling along coupling vectors
- N = 1 sets the number of radial grid points to a minimum (the grid is not needed when employing GTO and HF)
cartPOS and cartVEL. These give the intial positions and velocities of the atoms.

Running hole-state dynamics

To run the first example, execute:

xpyder -i input_hole_gto -d hole_gto

Output data for hole-state dynamics

The folder hole_gto contains output files.

R.log contains the position of the atoms for each time step.
V.log contains the velocity of the atoms.
E.log contains the current potential energy, kinetic energy and total energy of the trajectory.
Switch.log contains information about surface hops
S.log contains information about the current state index
C.log state coefficients
P.log state populations
V_ad.log adiabatic potential energies as a function of time
partial.log shows partial charges (Mulliken charges) for different time steps

Potential energy for the considered electronic hole states as a function of time for a sample trajectory. The red dash-dotted line marks the active state.

Details of the Inputfile input_cis

The file input_cis_gto addresses the dynamics of a water molecule in the excited state. The excited state is described using configuratios interaction singles. The following sections are modified compared to the earlier input file:

$xmolecule
  gto = 6-31G_star_star
  HF = yes
  CIS = yes
  nstates = 10
$end

$quantum
   type = fssh
   nstates = 10
   istate  = 3
   rescaling = nac
   N = 1
$end

In the section $xmolecule, the line CIS = yes switches on configuration interaction singles calculation, nstates = 10 indicates that up to 10 states are calculated. In the section $quantum, the parameter “nstates” was set to 10 (the same number as in the section quantum), and “istate” is set to 3 (the initial state), which means the 3rd excited state (0 means ground state).

Running the FSSH CIS excited-state trajectory

To run the second example, execute:

xpyder -i input_cis_gto -d cis_gto

Output data for FSSH CIS excited-state trajectory

The folder cis_gto contains the same output files as for the early run for the ionized state.

Potential energy for the considered electronic excited states as a function of time for a sample trajectory. The red dash-dotted line marks the active state.

Details of the Inputfile for trivial crossing detection

The file input_cis_olap_gto adds a scheme, in which state overlaps are calculated in each step of the MD calculation. This identifies trivial crossings along the trajectory. In order to do so the option:

trivialCrossing = overlap

is added to the $quantum parameter section.

Running the dynamics: detection of trivial crossings

To run the example, execute:

xpyder -i input_cis_olap_gto -d cis_olap_gto

Output data: detection of trivial crossings

In the folder cis_olap_gto, the additional file V_cross.log contains potential energies as a function of time without trivial crossings. Note that the order of state can change! The additional file trivialCrossings.log logs the appearance of trivial crossings.