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本帖最后由 LGC020305 于 2020-10-6 05:06 编辑
1. 给你转一段社长的答复（不针对你的具体问题）： https://www.researchgate.net/pos ... gaussian-16_package
17th Dec, 2017
Tian Lu， Beijing Kein Research Center for Natural Sciences
The number of core orbitals of each element is already known according to chemistry knowledge, since lowest lying MOs are mainly composed of core atomic orbitals, the number of lowest MOs to be frozen can be simply obtained by counting all core orbitals of atoms presented in current system.
By default, in Gaussian, all atomic orbitals except for the outermost valence ones are regarded as core atomic orbitals. This typically works reasonably. However, in rare case this treatment may cause unsatisfactory result; for example, if you optimize Li2, you will find the discrepancy between CCSD(T,full) and CCSD(T) is never small. Because Li only has one valence electron, electron correlation due to its 1s electrons also have nonnegligible contribution to chemically interesting quantites.
In Gaussian there are a few different ways of determining how many orbitals will be frozen, see http://gaussian.com/frozencore/. For example, with "FreezeInnerNobleGasCore" keyword, MOs composed of both outermost valence and sub-valence atomic orbitals will not be frozen.
If you are still confusing, you can try to calculate some elements and simple molecules, the number of frozen MOs can be found after "NFC=" label in output file.
2. Full
This specifies that all electrons be included in a correlation calculation.
FC
This specifies a “frozen core” calculation, and it implies that inner-shells are excluded from the correlation calculation. This is the default calculation mode.
3. 好比如一个是近似解，另一个不是。理论上Full 的更可靠 |
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发表于 Post on 2020-10-6 00:51:16
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发表于 Post on 2020-10-7 00:38:36