Isotopic Substitution (Optional)

Obtaining frequencies and intensities for isotopically substituted compounds can be performed a number of ways. The method shown below is best since it has three distinct steps common to all methods, and gives unambiguous assignments of modes to frequencies.

First, copy input.dat, intco.dat(if necessary), file11.dat, file15.dat, and a file17.dat into a working directory. These are the data of the unsubstituted isotopomer. The equilibrium geometry must be at the top of the file11.dat.

Next, add masses array to intder. Remember, intder will not check the default section for a masses array, just intder.

intder: ( 
 
masses = (      ) 
  )

Transform the dipole moment derivatives from cartesian to internals by modifying intder.

intder: ( 
 derlvl = 1 
 trans_1der = false 
 trans_type = c_to_i 
 trans_dipder = true 
 multi = 1  
 irint_t = none 
 freq_anal = none 
 masses = (      ) 
)

Type intder to generate a file18.dat.

Then, transform the second derivatives of the energy from cartesian to internals.

intder: ( 
 derlvl = 2 
 trans_1der = true 
 trans_type = c_to_i 
 trans_dipder = false 
 multi = 1 
 irint_t = none 
 freq_anal = none 
 masses = (    ) 
)

Type intder to generate a file16.dat.

Finally, carry out the calculation of the frequencies and intensites in both cartesian and internal space.

intder: ( 
 derlvl = 2 
 trans_1der = false  
 trans_type = i_to_c  
 trans_dipder = false 
 multi = 1 
 irint_t = do  
 freq_anal = both  
 masses = (    ) 
)

Type intder to calculate frequencies and intensities and append them to output.dat.