Module 2 : Ab inito methods and applications
Chapter 25 : Hessian Calculations and Simulation of IR Spectra
 
25.2 Calculation of vibration frequency
The following INPUT is prepared for a hessian calculation. The input is essentially the same as in case of geometry optimization except that the input geometrical parameters have to be the final optimized one at the same level of theory. It is the requirement of theory as explained in the previous section that at the equilibrium geometry only the gradient is zero. In the present case, we consider the final optimized structure of H2O molecule calculated at B3LYP/6-31++G(d,p) for hessian calculation. The input consider for this calculation is as follows.

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$SYSTEM TIMLIM=6000.0 MWORDS=11 MEMDDI=90 $END
$CONTRL SCFTYP=RHF MPLEVL=0 MAXIT=100 ICHARG=0 MULT=1
COORD=ZMT RUNTYP=HESSIAN TDDFT=NONE $END
$DFT DFTTYP=B3LYP METHOD=GRID $END
$SCF DIRSCF=.F. DAMP=.T. SHIFT=.T. $END
$BASIS GBASIS=N31 NGAUSS=6 NDFUNC=1 NPFUNC=1 DIFFSP=.T. DIFFS=.T. $END
$DATA
water: hessian//B3LYP/6-31++G(d,p)
CN 1

O
H    1    roh
H    1    roh    2    ahoh
roh=0.96 55191                                                
ahoh=105.7086105
$END
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