About the relation between Paritition and LnPartition for NH3

[w_wonder]

From https://github.com/iRASPA/RASPA2/blob/master/examples/Tutorial/ReactionEnsembleAmmonia/simulation.input

"

Component 2 MoleculeName NH3 

 

 MoleculeDefinition Local 

 

 LnPartitionFunction 253.69"


 From

https://github.com/iRASPA/RASPA2/issues/4 and
https://github.com/iRASPA/RASPA2/files/3927153/RASPA.Ammonia.Synthesis.Partition.Function.pdf

Table 2,
"NH3 1.8118E+02 1.9951E+02 1.1422E+00 4020.5 1.66002E+08 1.498133E+08"

The partition function seems to be ~ 1*10^8. I calculated the partition function of NH3 using quantum chemistry software and got ~ 10^8 value.


 I am unable to relate 253.69 to ~1*10^8, for example, from https://www.rapidtables.com/calc/math/Ln_Calc.html

ln(1.498133e8) gives me ~ 18.82.

 May I know how the partition function and LnPartitionFunction are related? Thanks

[David Dubbeldam]

These value come from: https://pubs.acs.org/doi/suppl/10.1021/acs.jctc.7b00092/suppl_file/ct7b00092_si_001.pdf
and to reduce under/overflow you input them as the log of these numbers in Table S3.

[w_wonder]

Thanks a lot. Sorry I am still confused 

Would you provide any page number for McQuarrie8 used in Table S3 and/or calculation steps? Molecular thermal wavelength from https://en.wikipedia.org/wiki/Thermal_de_Broglie_wavelength is about 10^-11 m ~ 0.1 angstrom at 298K. q/\Lambda^3 ~ q/0.1^3 is unlikely to provide 10^100 for NH3, even varying mass and temperature.

[David Dubbeldam]

For a detailed explanation see:
https://homepage.tudelft.nl/v9k6y/thesis-Rahbari.pdf
Page 262 and following, and see Table  A5.

[w_wonder]

Thanks.

Looks like exp(D0/kT) and total atomic energy are the keys. I managed to verified ~ 20%.

[w_wonder]

Hi, one more question, in https://github.com/iRASPA/RASPA2/blob/master/examples/Tutorial/ReactionEnsembleAmmonia/simulation.input
ExternalPressure 4e7

but, for the data in Table A5 https://pure.tudelft.nl/ws/portalfiles/portal/71296377/Thesis_Ahmadreza_Rahbari.pdf
I can reproduce (~20% accuracy) with 1e5 pressure (standard) based on Gaussian output (multiplying /V and exp(beta T) terms; V = RT/p), if I use 4e7, that will lead to orders of magnitude difference.

Question 1: for the data in Table A5, what pressure was used?
Question 2: if the answer to question 1 is the standard pressure, does the partition function needs to be consistent with ExternalPressure? If the answer to question 1 is the ExternalPressure, how it was evaluated?
Thanks

[w_wonder]

These value come from: https://pubs.acs.org/doi/suppl/10.1021/acs.jctc.7b00092/suppl_file/ct7b00092_si_001.pdf
and to reduce under/overflow you input them as the log of these numbers in Table S3.

One more question. Does RASPA have two conventions in the partition function, that previously, the exp(D0/kT) term was not included
as in https://pubs.acs.org/doi/suppl/10.1021/acs.jctc.5b00160/suppl_file/ct5b00160_si_001.pdf
later the exp(D0/kT) was included, as in
https://pure.tudelft.nl/ws/portalfiles/portal/71296377/Thesis_Ahmadreza_Rahbari.pdf

Thanks.