What is a good open source software for calculating the rotational and translational entropy of molecules? The National Institute of Standards and Technology does not provide standard molar entropy for all molecules.
4 Answers
ASE: Thermochemistry module
The thermochemistry module of ASE is able to calculate these for you.
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5$\begingroup$ Just to remember that ASE, by it self, doesn't do any calculation. It needs external calculators. The included calculator EMT is a simple calculator recommended only for quick demonstrations and tests. $\endgroup$– Camps ♦May 18, 2020 at 14:13
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2$\begingroup$ True, but in this case the module actually does a bit of calculating itself. It takes the potential energy and the vibrational energies to calculate the thermodynamic quantities. Of course you still need a code to calculate the former. But ASE interfaces to multiple open source options there. $\endgroup$ May 19, 2020 at 15:42
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$\begingroup$ Not quite sure I understand what you want to show. It's very unconvenient since the link is not clickable anymore, but if it helps you sure... $\endgroup$ Jul 1, 2020 at 8:06
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$\begingroup$ @patrickmelix I have converted it back. For some reason, the system still didn't like it. The site has a tour page that uses an example question to explain the site to new user. For whatever reason, its very strict about what sort of formatting these posts can have. I finally found another question that didn't require ugly hacks to get it to fit. $\endgroup$– Tyberius ♦Jul 3, 2020 at 18:37
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).
The rotational entropy derives from the moments of inertia, through the rotational partition function as well as any symmetry of the molecule. So you'll want to make sure you have a fairly accurate geometry, optimized using that particular method, to get accurate moments of inertia.
Here's an example using the xtb
program - I'm analyzing these for a paper:
temp. (K) partition function enthalpy heat capacity entropy
cal/mol cal/K/mol cal/K/mol J/K/mol
298.15 VIB 0.350E+07 10585.483 74.558 62.428
ROT 0.115E+08 888.752 2.981 35.294
INT 0.404E+14 11474.235 77.539 97.722
TR 0.626E+28 1481.254 4.968 43.410
Here you want the VIB, ROT, and TR entropies for the vibrational, rotational, and translational entropy.
Any molecular quantum program that I've used will spit these out after performing a vibrational calculation. The format of the output varies, though.
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$\begingroup$ I'm checking - in principal, the
cclib
package helps parsing entropies, although I haven't used it. $\endgroup$ May 19, 2020 at 17:03 -
$\begingroup$ Better make sure your geometry is a minimum for the method; otherwise the vibrational calculation makes very little sense.. $\endgroup$ May 24, 2020 at 15:56
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$\begingroup$ @SusiLehtola - 100% agreed - I think it's already above in bold: "critical task is to start with an optimized geometry with a good method". I didn't see this mentioned in the other answers, thus I wrote one. $\endgroup$ May 25, 2020 at 14:40
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/thermo.html#examples
- And of course, there is the beautiful open source NWChem - which is actively developed at PNNL! It can do all sorts of calculations like Gaussian. See for more details: https://nwchemgit.github.io/
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)
*********************************************************************************************************
o methylaniline -326.664901 0.135012 -326.521265 0.040238 0.040091 -326.561503 -326.561356
*********************************************************************************************************
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1$\begingroup$ It also seems to supports ORCA and NWChem output files. It's moreover highly customizable and supports approximations beyond RRHO. $\endgroup$– KexanoneMar 13, 2021 at 19:16