<div dir="ltr">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 </div>