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13

ASE: Thermochemistry module The thermochemistry module of ASE is able to calculate these for you.


10

Any quantum chemical program should calculate these for you as part of a vibrational calculation. Generally, the vibrational, rotational, and translational entropies will be given. The critical task is to start with an optimized geometry with a good method - and ideally some level of conformer search (i.e., to make sure you have a low-energy conformer). ...


9

Psi4 and NWChem For open source software to perform this task, I can think of Psi4. It's probably the easiest to download/install and get going. It has the usual computational chemistry methods along with ab-initio/SAPT methods. Some details can be found here: psi4: http://www.psicode.org/ psi4 thermochemistry: http://www.psicode.org/psi4manual/master/...


9

tldr, Extensively sample the potential energy surface of the molecule, then Boltzmann-weight the relative energies. The CREST tool is useful. Nice to see this question as I'm writing / editing a paper on the conformational entropy of molecules. There's already a question about the translational and rotational entropy of molecules. For those, you optimize a ...


7

Always use the energy after extrapolation back to 0 K. The energy before the extrapolation is just from your smearing method and is a fictitious value.


5

I'll try to summarize the argument mentioned in the comments from Daniel Schroeder's Introduction to Thermal Physics. Your derivation is correct within a certain approximation commonly made when dealing with atomic sized systems. Consider an isolated system of an hydrogen atom in thermal equilibrium with a reservoir (which could in principle be the rest of ...


4

GoodVibes GoodVibes is able to calculate what you want from Gaussian logfiles. From its documentation (using scaled vibrational frequencies): python -m goodvibes examples/methylaniline.out -v 0.95 Structure E ZPE H T.S T.qh-S G(T) qh-G(T) ***************************************************...


4

Just throwing a couple of ideas out there: (i) Perform a free energy perturbation or potential of mean force calculation as available in typical classical MD setups. For known salt systems in water, this is well studied and should result in decent results (e.g., Joung and Chaetham's paper). (ii) Do a classical MD in explicit solvent for the solute of ...


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