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标题: Energy refinement at different basis set [打印本页]

作者
Author: zako 时间: 2025-2-3 04:55
标题: Energy refinement at different basis set
Hello everyone,
I have studied a chemical organic reaction catalysed by the Lewis acid "SnCl4" using DFT methods. I have used mixed basis sets (6-311G(d,p) for the atoms C, H, O and Cl; and SDD for Sn atom). Is it possible to make energy refinement by performing a single point calculations at the advanced basis set Def2-TZVPP? If yes, what's the best way, Def2-TZVPP for all the atoms, or keep 6-311G(d,p) for the atoms C, H, O and Cl; and Def2-TZVPP for only Sn atom?

Many thanks in advance

作者
Author: dnlx 时间: 2025-2-3 10:28
Other than the Sn atom, you should use the better basis set at least for any other atoms involved in bond formation or breaking in your reaction. Therefore, "Def2-TZVPP for all the atoms" is better than "Def2-TZVPP for only Sn atom".

作者
Author: sobereva 时间: 2025-2-3 16:55
If you can easily afford the cost, simply using def2-TZVPP for all atoms is certainly the best choice.

作者
Author: zako 时间: 2025-2-3 19:08
Thank you all very much for your valuable answers, and i would like to inquire about :
1- Isn't there any issue or contradictions performing single-point energy calculation using "Karlsruhe basis set" (Def2-TZVPP), despite i performed the optimization calculations using "pople basis set (6-311G(d,p) and ECP basis set (SDD))" ?
2- Concerning the thermochemical values (Enthalpy, Entropy and Free Gibbs Energy), Can i use the electronic energy obtained using (Def2-TZVPP) to calculate a new the thermochemical values ? i mean add the new electronic energy to the old thermal corrections to get new values of thermochemical values. Is it a safe and correct procedure erroneous ?

作者
Author: dnlx 时间: 2025-2-4 04:26
本帖最后由 dnlx 于 2025-2-4 04:30 编辑

zako 发表于 2025-2-3 19:08
Thank you all very much for your valuable answers, and i would like to inquire about :
1- Isn't the ...

1. No issues or contradictions.
2. Yes you can and you should. This is a standard practice. See the second note on this page
https://www.faccts.de/docs/orca/5.0/tutorials/prop/thermo.html

This G-E(el) only depends on the geometry and frequencies, and thus can be computed in a lower level method, such as DFT, and later combined with the Eel
of a higher level method, such as DLPNO-CCSD(T) to achieve a very good prediction of the G0

作者
Author: zako 时间: 2025-2-5 06:47
本帖最后由 zako 于 2025-2-5 07:05 编辑

dnlx 发表于 2025-2-4 04:26
1. No issues or contradictions.
2. Yes you can and you should. This is a standard practice. See t ...

Dear dnlx, Thank you very much
Since you mentioned the DLPNO-CCSD(T) method for single point energy calculations, which is only can be used in ORCA program, i would like to how to switch from Gaussian calculations, since i performed the optimisation and vibration calculations using Gaussian package to Orca DLPNO-CCSD(T) calculation ?

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