From NWChem
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8:24:18 AM PDT  Mon, Mar 16th 2015 

Hi.
Rotation entropy of molecule depends on its pont group and symmetry number thereof, as described http://cccbdb.nist.gov/thermo.asp (eq 19), but when using CCmethods only abelian point groups is allowed.
In the case of highly symmetric compounds such as cubane or dodecahedrane incorrect values of rotation entropy are obtained.




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8:15:18 PM PDT  Wed, Mar 18th 2015 

reusing existing hessian with proper symmetry group solve the problem.




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11:34:18 PM PDT  Wed, Mar 18th 2015 

Hi Vladimir,
I am glad that you were able to solve this problem. Could you post an example input file demonstrating your solution? I will want to perform similar calculations in the future.
Thanks,
Matt




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9:00:38 AM PDT  Thu, Mar 19th 2015 

Quote:Mernst Mar 19th 1:34 pmHi Vladimir,
I am glad that you were able to solve this problem. Could you post an example input file demonstrating your solution? I will want to perform similar calculations in the future.
Thanks,
Matt
Hi Matt, here is an example.
As described in http://www.nwchemsw.org/index.php/Vibration I reuse the previously computed hessian by specifying "reuse" in the "freq" module input block.
title "N8cubane CCSD/ccpVDZ hessian"
memory stack 100 mb heap 100 mb global 100 mb
geometry
symmetry Oh
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
N 0.76104280 0.76104280 0.76104278
end
freq
reuse N8.hess
end
task tce freq
It is important that the order of the atoms during the calculation of hessian and its subsequent reusing were exactly the same. Check it out in the output file.



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