<div>The frequencies and the reduced masses are very similar in both Gaussian and CP2K.(probably because both of them report in the same units).</div><div> </div><div>I've included for you the CP2k input for frequency cal.</div><div> </div>&GLOBAL PROJECT H2O RUN_TYPE VIBRATIONAL_ANALYSIS PRINT_LEVEL MEDIUM &END GLOBAL &FORCE_EVAL METHOD QS &DFT BASIS_SET_FILE_NAME BASIS_MOLOPT POTENTIAL_FILE_NAME GTH_POTENTIALS CHARGE 0 MULTIPLICITY 1 &PRINT &MOMENTS &END &END &MGRID CUTOFF 300 NGRIDS 5 REL_CUTOFF 70 &END MGRID &QS EPS_DEFAULT 1.0E-12 WF_INTERPOLATION ASPC &END QS &SCF SCF_GUESS ATOMIC EPS_SCF 1.0E-7 MAX_SCF 1000 CHOLESKY INVERSE ADDED_MOS 50 &DIAGONALIZATION ALGORITHM STANDARD &END DIAGONALIZATION &MIXING METHOD BROYDEN_MIXING ALPHA 0.4 NBROYDEN 8 &END MIXING &END SCF &XC &XC_FUNCTIONAL &PBE &END PBE &END XC_FUNCTIONAL &vdW_POTENTIAL DISPERSION_FUNCTIONAL PAIR_POTENTIAL &PAIR_POTENTIAL PARAMETER_FILE_NAME dftd3.dat TYPE DFTD3 REFERENCE_FUNCTIONAL PBE R_CUTOFF 15.0 &END PAIR_POTENTIAL &END vdW_POTENTIAL &END XC &POISSON PERIODIC xyz POISSON_SOLVER WAVELET &END POISSON &END DFT &SUBSYS &CELL ABC 20.0000 20.0000 20.0000 ALPHA_BETA_GAMMA 90.0 90.0 90.0 PERIODIC xyz &END CELL &COORD O -0.762288846626 0.000000000001 -1.462238785752 H -0.762288846634 0.759337000000 -0.866195785751 H -0.762288846634 -0.759337000000 -0.866195785753 &END COORD &KIND Mg BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE-q10 &END KIND &KIND O BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE-q6 &END KIND &KIND Y ELEMENT Y BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE-q11 &END KIND &KIND C ELEMENT C BASIS_SET DZVP-MOLOPT-GTH POTENTIAL GTH-PBE-q4 &END KIND &KIND H ELEMENT H BASIS_SET DZVP-MOLOPT-GTH POTENTIAL GTH-PBE-q1 &END KIND &END SUBSYS &END FORCE_EVAL &VIBRATIONAL_ANALYSIS FULLY_PERIODIC INTENSITIES NPROC_REP 4 &END VIBRATIONAL_ANALYSIS &MOTION &CONSTRAINT &FIXED_ATOMS &END FIXED_ATOMS &END CONSTRAINT &GEO_OPT OPTIMIZER LBFGS TYPE MINIMIZATION MAX_DR 4.5E-4 MAX_ITER 500 &END GEO_OPT &END MOTION <div class="gmail_quote"><div dir="auto" class="gmail_attr">On Saturday, August 23, 2025 at 7:45:05 PM UTC+5:30 Naina Sethi wrote: </div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Dear all, I am working on calculating the vibrational frequencies and force constants of a water molecule. In CP2K, the force constants are reported in atomic units (Hartree/Bohr²), while Gaussian lists them in mDyne/Å. The conversion factor between Hartree/Bohr² and mDyne/Å is about 15.57. However, even after applying this factor, the results from CP2K do not match the force constant values reported by Gaussian. Could anyone clarify why this discrepancy occurs? <div> </div><div> Frc consts -- 1.7016 8.9360 9.7649 (gaussian)</div><div> VIB|Frc consts (a.u.) 0.017668 0.567398 0.663392 (CP2K)</div><div> </div><div>Thanks and Regards</div><div>Naina</div></blockquote></div> -- You received this message because you are subscribed to the Google Groups "cp2k" group. To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:cp2k+unsubscribe@googlegroups.com">cp2k+unsubscribe@googlegroups.com</a>. To view this discussion visit <a href="https://groups.google.com/d/msgid/cp2k/184f6f3d-8736-42fb-9c42-bb8cbd906defn%40googlegroups.com?utm_medium=email&utm_source=footer">https://groups.google.com/d/msgid/cp2k/184f6f3d-8736-42fb-9c42-bb8cbd906defn%40googlegroups.com</a>.