Setting up perturbative Delta SCF calculation with previous versions of NRLMOL

Running excited state calculations using perturbative delta SCF method. This is not automated yet so use the following guidelines to run the excited states calculations. The method works well for the charge transfer excited states. It is a perturbation approach, so the first step is to carry out the ground state SCF. Run a spin-polarized ground state calculation for a chosen system without using any point group symmetry. Each excited state calculation is done in a separate directory. Use the following procedure to run the excited state calculations.

1. Make a directory, say EXCITED1 and copy the following files from the directory where the ground state calculations were performed to the excited state directory: SYMBOL, GRPMAT, ISYMGEN, HAMOLD, REPMAT, VMOLD.

2. Create RUNS file. Your RUNS file for the excited state calculation should be:

       -1     N            ITBEG, NCALC
        1     4            START: 0=SCR.NUC, 1=HAM, 2=POT, 3=LSF, 4=WFUNC
        0                  START HAMILTONIAN IS INTERPOLATED: 0=NO, 1=YES
   

   where, N is the geometry number of the corresponding geometry in SYMBOL. “-1” option allows previously generated mesh; if, for some reason, this does not work, then set it to “1” and rerun. WARNING Most of the problems/errors with excited states calculation are due to use of different geometries in the excited state and the ground state. So please ensure that you use correct geometry:- the second field in the top line of the RUNS file. Also, for the excited state calculation with perturbative delta SCF method, you always start with Hamiltonian.

3. Run the command “$ echo ”.TRUE.” > RUNTYPE

4. Next create a file called OCCEXC with required occupation numbers. (No blank lines). An example OCCEXC for the water molecule (H2O) is given below:

    1      : Number of excited states to be calculated. For starter keep it 1.
    -76.387242322234A     : Ground state SCF energy
   1 5                    : Spin and state indices for the hole
   2 6                    : SPin and state indices for the particle
   5                      : Number of GS occupied orbitals of spin 1
   1 1 1 1 1              : GS occupancy of the states of spin 1
   5                      : Number of GS occupied orbitals of spin 2
   1 1 1 1 1              : GS occupancy of the states of spin 2
   5                      : Number of excited occupied orbitals of spin 1
   1 1 1 1 0              : occupancy of the orbitals of spin 1 in excited state
   6                      : Number of excited occupied orbitals of spin 2
   1 1 1 1 1 1            : occupancy of the orbitals of spin 2 in excited state
   

5. Compile the NRLMOL for the excited states. Your executable for the ground state may not work as the parameters are different for the excited states. When compiled, copy the executable here and submit the job.

TIP The memory demand for the excited state calculation is much larger than the ground state as both the ground

and excited state Hamiltonians are required. If your calculations run out of memory, one possibility is to use fewer cores per node in a parallel job.