UT theoretical chemistry code forum

Dear All,

I ran Ci-NEB for H migration energy barrier calculations and got the results. In the second step, I need zero point energy corrected energy barrier values so I ran dynamical matrix calculations using structures from my NEB calculations. Since my supercell contains 54 iron atoms and 1 hydrogen, I included 55 atoms for the generation of the DISPLACECAR file with a displacement of 0.05. Moreover, I have subdirectories numbered 01 to 03 where 01 is the initial structure and 03 is the saddle point. After the calculation was finished, first I ran dymmatrix.pl for initial and saddle point OUTCAR files, and then I used "dymeffbar.pl" script to see the final results, however, I got an error "Illegal division by zero at ./dymeffbar.pl line 81.". I think the problem occurred since I have so many 0 values in my freq.dat files but I am not sure. Could you please help me?

I think that you are right. That ZPE script just calculates quantum harmonic corrections to TST, so zero or negative modes will lead to a divergence. If you can identify 3 translational modes at both the reactant and saddle, as well as (perhaps) 3 rotational modes, you can simply remove them and run the script with a reduced set of only positive vibrational modes.