How to calculate the energy barrier at certain temperature

hlzya · Post by **hlzya** » Fri Sep 28, 2007 2:38 am

Hi,

Using the NEB or dimer method, I can get the energy barrier at 0 K, right? However, if the temperature of reaction is very high, e.g. 1200 C, how can I get the energy barrier at that temperature, although the energy barrier is almost constant in a small temperature range.

Thanks.

Yi-An

Post by **graeme** » Sat Sep 29, 2007 4:06 am

Within harmonic transition state theory (TST), the energy barrier can be used to derive the Arrhenius rate = A exp (-dE/kT) , where dE is the energy barrier. This is an approximation which gives a rate at all temperatures, but that is more accurate a low temperature. Here, the energy (enthalpy) barrier is not temperature dependent.

It is also possible to use a more general form of TST in which you sample a free energy barrier. While this is possible, we do not provide tools for doing it within vasp.