Anharmonic Partial Hessian Vibrational Analysis

Dear Q-Chem community,

I am using Q-Chem version 5.4.0 to perform a partial Hessian vibrational analysis, and I would like to calculate anharmonic (TOSH and VPT2) frequencies for the vibrational modes found in the harmonic partial Hessian calculation. From reading the Q-Chem manual, it seems like this is possible, but there are no examples.

Below I include a representative input file for a successful partial Hessian harmonic frequency calculation:

0 1
H         0.0000000000    0.0000000000    1.6627839987
C         0.0000000000    0.0000000000    0.5996740432
C         0.0000000000    0.0000000000   -0.5996740432
H         0.0000000000    0.0000000000   -1.6627839987

BASIS  =  6-311++G**
JOB_TYPE  =  freq
THRESH  =  14
XC_GRID = 000099000590
PHESS = True
N_SOL = 3


The Q-Chem manual indicates that I can follow a partial Hessian calculation with VPT2 and TOSH anharmonic frequency calculations, so I tried adding the keyword ANHAR = True to the $rem section of the above input file, but I received the following error:

Q-Chem fatal error occurred in module libmdc/newfileman.C, line 384:

 FileMan error: End of file reached prematurely reading (1152) bytes in file FILE_NORMAL_MODE

Any guidance to help me calculate anharmonic frequencies for a partial Hessian is very much appreciated!

There is nothing wrong with your input, there is indeed a bug somewhere. I’ve filed a ticket in our issue tracker. Do you have any older versions of Q-Chem available to you?

Hi Eric,

Thanks for your reply! I have access to Q-Chem version 5.3 but nothing older. I checked the calculation on v. 5.3, and got the same error.

Clyde Daly is my PI (he says hi!) and he thinks he was able to do a version of this calculation on Q-Chem v. 4, if that helps narrow down the bug.