I will use DFT calculation tool, MedeA VASP, for calculating Gibbs free energy of gas phase and solid phase.
I know that gas phase calculation using VASP may be uncorrect. But I can't use Gaussian because of the budget.
MedeA VASP Phonon module gives below data
1)Cv : vibrational heat capacity at constant volume 2)E_vib(T)=E(T)-E(0) : the change in vibrational internal energy from 0 K, where E(0) = E_elec + ZPE is the electronic energy of formation E_elec plus the zero point energy ZPE 3)S(T) : the vibrational entropy at temperature T 4)-(A(T)-E(0)) : the change in the vibrational Helmholtz free energy from 0 K 5)E(T) : the electronic energy of formation plus the vibrational internal energy, so this term is E_elec + ZPE + E_vib(T)
6)A(T) : the electronic plus vibrational Helmholtz free energy, E(T) - T.S(T)
and my questions are
1)How can I calculate Gibbs free energy for gases and solids from these data?
(I know that in a gas we can regard the internal energy as the sum of the electronic, translational, rotational, and vibrational energies. And We just get electronic and vibrational energy. Also, How can I consider PV term?)
2)How accurate is the VASP transition state and thermodynamic calculation for gas?
(I will calculate reactions for CVD reaction. ex)SiH4+SiH4->SiH6+H2, Si(wafer)+SiH4->Si+H2, etc.)
As you mentioned it. The gas phase in VASP may be incorrect. An easy way to do the solid phase and gas phase could be:
1. Solid phase: compute the vibrational frequencies of the system. With that, you could calculate the enthalpy=U+KbT+H_vib., and then the Gibss as H-TS (Article Molecular Spin Crossover Materials: Review of the Lattice Dy...
)2. Gas phase: You could follow the tutorial of ORCA (free software: https://www.orcasoftware.de/tutorials_orca/prop/thermo.html). You must construct a good (and representative) model of your system in gas phase.
- Badges
- Science topic