UT theoretical chemistry code forum

Hi Sir,
I am doing dimer calculation. I want to do zero point energy correction to the reaction coordinates using vasp . Can you give me some advice? Thank you !

The simplest correction is to add hv/2 for each positive mode at stationary points. The frequencies, v, can be found using a dynamical matrix calculation. Once you have the eigenvalues, we do have a script called dymzpbar.pl, which will do this calculation.

A better approximation is based upon the quantum harmonic partition function, because it has the proper form at high temperature. A script for doing this is dymqeffbar.pl. There are many references for this, but one example from our group can be found in:

http://theory.cm.utexas.edu/henkelman/p ... 044706.pdf

Another contribution to the quantum rate is due to tunneling at the saddle. This same reference describes the Wigner harmonic correction (again, there are many other references for this). This correction is good at high temperature, but at low temperature (especially near and below the crossover temperature), an anharmonic treatment, such as the Eckart correction, is needed.

The scripts can be downloaded from:

http://theory.cm.utexas.edu/vtsttools/scripts/