Vibrational spectra of methane

To calculate the vibrational spectra of a molecule you first need to calculate an optimised geometry, as shown in the previous section. Once you have an optimised geometry, you call the specsym program as follows

specsym VIBINP F F F 1 > specsym.out

This will create several files, the most important of which is SYMVIB. This is SYMBOL file with a number of calculations to be performed using cluster. Before running these calculations some files will have to be rearranged, and it is a good idea to do more than just the minimum, as you want to keep the results of the geometry optimisation. The following is the recommended minimum

cp EFIELD   EFIELD.GEO
cp EVALUES  EVALUES.GEO
cp FRCOUT   FRCOUT.GEO
cp GRPMAT   GRPMAT.GEO
cp SCFDAT   SCFDAT.GEO
cp SYMBOL   SYMBOL.GEO
cp VIBINP   VIBINP.GEO
cp XMOL.DAT XMOL.GEO
cp GRPVIB   GRPMAT
cp SCFDVIB  SCFDAT
cp SYMVIB   SYMBOL
mv GEOCNVRG GEOCNVRG.GEO
mv ATOMSPH  ATOMSPH.GEO
mv DOSJNT   DOSJNT.GEO
mv DOSOCCU  DOSOCCU.GEO
mv DOSVIRT  DOSVIRT.GEO

Now you have to run cluster once for each calculation in the new SYMBOL file, and store the resulting FRCOUT from each calculation. This can be done using the following command

rm -f SUMMARY; cluster; cat FRCOUT >> allfrcout;

for each calculation. Once all the calculations have been run, the results get fed back into specsym using the following command after rearranging the files again as follows

cp EFIELD.GEO  EFIELD
cp EVALUES.GEO EVALUES
cp FRCOUT.GEO  FRCOUT
cp GRPMAT.GEO  GRPMAT
cp SCFDAT.GEO  SCFDAT
cp SYMBOL.GEO  SYMBOL
cp VIBINP.GEO  VIBINP
cp XMOL.GEO    XMOL.DAT
cat allfrc.out >> VIBINP
specsym VIBINP T T F 3 > specsym.out