IP as CV and much much ... much more

[Teodoro Laino]

Dear All,

as a follow-up on the request of Peter of using the ionization potential as CV, I decided to implement this feature together with an infinite amount of other feasible combination.
The trick is in using the MIXED force_eval: you can specify one force_eval for a neutral specie and another for the same specie with a -1 charge, and use the difference between the two energies as a CV (it is implemented again the possibility to specify whatever functions of the energy).

There are many other possibilities one can do:
-) use different subsystems
-) use different Hamiltonians
-) use excited states and differences between excited states to explore conical intersections (when these will be available in cp2k!.. so not yet at the moment)

Again.. as usual.. the only limit is your imagination. I hope you all enjoy this little programming effort.
For any question/request, do not hesitate to contact me.

Regards to all,
Teo

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As an example, the IP CV can be defined in the following way (tests/QS/regtest-meta/H2O-meta-IP.inp) :

#These computes the energies for the two systems
@SET CHARGE  0
@SET LSD 0
@include dft_force_env.inc
@SET CHARGE -1
@SET LSD 1
@include dft_force_env.inc

#this force_eval combines for the evolution of the EOM
&FORCE_EVAL
  METHOD MIXED
  &MIXED
    MIXING_TYPE GENMIX
    NGROUPS  2
    &GENERIC
      MIXING_FUNCTION E1+k*E2
      VARIABLES E1 E2
# Propagate the Equation of Motion according to the neutral state Hamiltonian by using only the energy of the charge == 0 system
      PARAMETERS k
      VALUES 0.
    &END
  &END
  &SUBSYS
    &CELL
      ABC 5.0 5.0 5.0
    &END CELL
    &COORD
      O   0.000000    0.000000   -0.065587
      H   0.000000   -0.757136    0.520545
      H   0.000000    0.757136    0.520545
    &END COORD
    &KIND H
      BASIS_SET DZVP-GTH-PADE
      POTENTIAL GTH-PADE-q1
    &END KIND
    &KIND O
      BASIS_SET DZVP-GTH-PADE
      POTENTIAL GTH-PADE-q6
    &END KIND
    &COLVAR
       &U
         &MIXED
# we define the difference of the two energies as CV.
# You can specify here in general whatever function you like!!!!!
           ENERGY_FUNCTION E2-E1
           VARIABLES E1 E2
         &END
       &END
    &END COLVAR
  &END SUBSYS
&END FORCE_EVAL