Gaussian 03 Online Manual
Last update: 29 September 2006

freqchk

The freqchk utility is used to retrieve frequency and thermochemistry data from a checkpoint file, with optional specification of an alternate temperature, pressure, scale factor, and/or isotope substitutions.

freqchk can prompts for all other information that it requires. The following annotated sessions illustrate its use in this mode (user input is set in boldface type):

$ freqchk 
 Checkpoint file? solvent.chk 
 Write Hyperchem files? n 
 Temperature (K)? [0=>298.15] 0          Zero must be entered; return doesn't work 
 Pressure (Atm)? [0=>1 atm] 0 
 Scale factor for frequencies during thermochemistry? [0=>1/1.12] 0 
 Do you want the principal isotope masses? [Y]:   Return accepts defaults 
  Isotopes for each atom are printed 
 Full mass-weighted force constant matrix: 
 Low frequencies --- -948.3077     .0008     .0020     .0026 
 ... 
 Normal Gaussian frequency output follows ... 
                       1                     2 
                      ?A                    ?A 
 Frequencies --  1885.3939             3853.5773 
 Red. masses --     1.0920                1.0366 
 Frc consts  --     2.2871                9.0697 
 IR Inten    --    17.3416               21.5997 
 Raman Activ --     7.8442               67.0384 
 Depolar     --      .7428                 .2248 
 Atom AN     X      Y      Z         X      Y      Z      Normal modes 
   1   8    .06    .00    .04       .04    .00    .02 
   2   1   -.70    .00    .03       .01    .00   -.71 
   ... 
 ------------------- 
 - Thermochemistry - 
 ------------------- 
 Temperature   298.150 Kelvin.  Pressure    1.00000 Atm. 
 Thermochemistry will use frequencies scaled by   .8929. 
 ... 
 Zero-point vibrational energy       53494.5 (Joules/Mol) 
                                       12.78550 (Kcal/Mol) 
 VIBRATIONAL TEMPERATURES:  2422.01  4950.36  5495.38 (KELVIN)      
                                Zero-point and thermal corrections: 
 Zero-point correction=                .020375 (Hartree/Particle) 
 Thermal corr to Energy=               .023210 
 Thermal corr to Enthalpy=             .024154 
 Thermal corr to Gibbs Free Energy=   .045589      
      E=thermal energy; CV=constant volume molar heat capacity; S=entropy 
                  E               CV                 S 
               KCAL/MOL    CAL/MOL-KELVIN   CAL/MOL-KELVIN 
 TOTAL          14.564          6.001             45.114 
 ELECTRONIC      .000            .000               .000 
 TRANSLATIONAL   .889           2.981             34.609 
 ROTATIONAL      .889           2.981             10.500 
 VIBRATIONAL   12.787            .039               .005     
      Partition functions 
                         Q              LOG10(Q)               LN(Q) 
 TOTAL BOT         .561443D-01          -1.250695           -2.880127 
 TOTAL V=0         .132155D+09           8.121085           18.699192 
 VIB (BOT)         .424961D-09          -9.371650          -21.579023 
 VIB (V=0)         .100030D+01            .000129             .000297 
 ELECTRONIC        .100000D+01            .000000             .000000 
 TRANSLATIONAL     .300436D+07           6.477751           14.915574 
 ROTATIONAL        .439749D+02           1.643204            3.783618 

$ freqchk solvent.chk                    Checkpoint filename can be placed on the command line 
 Write Hyperchem files? n 
 Temperature (K)? [0=>298.15] 300        Alternate temperature 
 Pressure (Atm)? [0=>1 atm] 1.5          Alternate pressure 
 Scale factor for freqs during thermochem? [0=>1/1.12] 1    No scaling 
 Do you want to use the principal isotope masses? [Y]: n 
 For each atom, give the integer mass number.
 In each case, the default is the principal isotope. 
 Atom number 1, atomic number 8: [16]    Return accepts default 
 Atom number 2, atomic number 1: [1] 2   Specify isotope masses as integers  
 ... 

Frequency output follows, reflecting the values specified above. Note that if scaling is specified, only the thermochemistry data reflects it; the frequencies themselves are not scaled.

Alternatively, you can specify all freqchk input on the command line, as in this example, which performs the same operation as the final interactive session above:

$ freqchk  solvent.chk N 300 1.5 1 N

You will be prompted for the isotopes if the final parameter is N.