questions about TDDFPT2

[NUCP2K]

Dear CP2K Developers and Users,

  I just tried out the latest implementation of time-dependent density 
functional perturbation theory (TDDFPT) in CP2K, and found some serious 
inconsistencies on the calculated excitation energy. 

  I tested the TDDFPT2 on an isolated water (H2O) molecule using the 
attached input file. Interestingly, the calculated excitation energy of 
10.075 eV  is much much greater than the HOMO-LUMO gap of 9.137 eV, even 
though the transition is dominated (>99.9%) by the electron transfer from 
HOMO to LUMO.  

  It seems to me that the diagonal terms of the TDDFPT response matrix are 
not appropriately assigned, leading to the apparent inconsistency. Perhaps, 
the subroutine "tddfpt_init_by_energy_diff" in qs_tddfpt2_methods.F should 
be fixed to yield correct orbital energy gap. 

  Please correct me if my understanding is wrong.

  Thanks.

Hanning


         &FORCE_EVAL
  METHOD QS
  &PROPERTIES
    &TDDFPT
     NSTATES      1
     MAX_ITER    100
     MAX_KV 10
     CONVERGENCE [eV] 1.0E-3
     &DIPOLE_MOMENTS
      DIPOLE_FORM LENGTH
     &END DIPOLE_MOMENTS
     &MGRID
      COMMENSURATE
      CUTOFF 50
     &END MGRID
    &END TDDFPT
  &END PROPERTIES
  &DFT
    BASIS_SET_FILE_NAME BASIS_SET
    POTENTIAL_FILE_NAME POTENTIAL
    &MGRID
      COMMENSURATE
      CUTOFF 50
    &END MGRID
    &POISSON
     PERIODIC NONE
     POISSON WAVELET
    &END POISSON
    &SCF
      SCF_GUESS ATOMIC
    &END SCF
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
      &XC_GRID
        XC_DERIV SPLINE2_SMOOTH
      &END XC_GRID
    &END XC
  &END DFT
  &SUBSYS
    &CELL
      ABC 6.0 6.0 6.0
      PERIODIC NONE
    &END CELL
    &COORD
   O     3.000000     3.000000     3.000000    H2O1
   H     3.000000     3.000000     4.000000    H2O1
   H     3.942809     3.000000     2.666667    H2O1
    &END COORD
    &KIND H
      BASIS_SET SZV-GTH
      POTENTIAL GTH-PADE-q1
    &END KIND
    &KIND O
      BASIS_SET SZV-GTH
      POTENTIAL GTH-PADE-q6
    &END KIND
    &TOPOLOGY
    &END TOPOLOGY
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PROJECT WATER
  PRINT_LEVEL MEDIUM
  RUN_TYPE ENERGY
&END GLOBAL
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