7 votes
Accepted

Frozen core Stability Calculations in G09?

A "frozen core" is used to freeze "core" electrons from correlating. There's no correlation in HF calculations, so it would make sense for a frozen core to only have a visible ...
Nike Dattani - No Free Time's user avatar
6 votes
Accepted

Calculate the energy of a single electron in an atom

Normally $\textit{ab initio}$ methods should give approximately the orbital energies that the electrons will occupy after applying the exclusion principle. The accuracy of the total energy is related ...
M06-2x's user avatar
  • 906
5 votes
Accepted

How do I get the energy, if I have the wavefunction?

"For a known wave function, should I not be able to determine the energy?" The wavefuncton is an eigenfunction of the Hamiltonian, and the energy is a corresponding eigenvalue of the same ...
Nike Dattani - No Free Time's user avatar
5 votes

Frozen core Stability Calculations in G09?

I think, the answer of @NikeDattani is clear enough a frozen core option should not be used for SCF methods as HF and even for DFT except for Double-Hybrid methods : MP Methods. Therefore your ...
M06-2x's user avatar
  • 906
4 votes
Accepted

Time Evolution of the Hartree-Fock Wave Function

In order to determine the time evolution of a Hartree-Fock state, the Time-Dependent Hartree-Fock (TDHF) method is indeed a suitable approach. TDHF is a mean-field method used to study the dynamics of ...
Sak's user avatar
  • 909
4 votes

Explicit form of Hartree Fock analytic gradient with contracted GTOs? With or without density fitting

Molecular Electronic-Structure Theory, by Helgaker et al., is an extremely comprehensive textbook reference for electronic structure on finite systems. I take the following from Section 10.8.3 (pp. ...
elutionary's user avatar
4 votes

Calculate the energy of a single electron in an atom

In Hartree-Fock theory, orbital energies are indeed good estimates for the energies of single electrons. This is because of Koopmans' theorem: if you assume that the other electrons do not relax when ...
Susi Lehtola's user avatar
  • 19.1k
3 votes

How do I get the energy, if I have the wavefunction?

UPDATE: I didnt read your post carefully enough. My answer is irrelevant. In your comment above you said I guess what i meant was that if I have an arbitrary state eigenfunction (approximated as the ...
Tyler Sterling's user avatar
3 votes

Post-hartree fock calculation with localized Molecular orbitals in PySCF

CCSD is invariant to a unitary transformation of the orbitals, as a localization is. You should thus get the same result with canonical and localized orbitals. However, since the CCSD amplitudes are ...
Frank Jensen's user avatar
  • 1,776
3 votes
Accepted

Molecular integrals in spherical harmonics?

Molecular integrals aren't typically computed in spherical harmonics. What you do instead is to compute the integrals in the Cartesian representation, where they are separable, and then transform to ...
Susi Lehtola's user avatar
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2 votes
Accepted

Is the Broyden's algorithm sufficient to obtain the crystal structure of a hypothetical alloy, or should something else be used?

BFGS is a local minimization method - it will find you the closest minimum to your starting structure - whereas finding the crystal structure is a global optimization problem: what is the structure ...
Susi Lehtola's user avatar
  • 19.1k
2 votes

What's the best code for getting 1-particle and 2-particle density matrices with CCSD(T) in Python?

With Psi4, I have been partially successful in obtaining the 1-PDM at the CCSD(t) level. Sharing the code, ...
Pro's user avatar
  • 964
2 votes
Accepted

Post-hartree fock calculation with localized Molecular orbitals in PySCF

Working input file and output Without changing your input lines for the HF calculation and the CCSD calculation without localization of orbitals, the following lines worked for doing CCSD with ...
Nike Dattani - No Free Time's user avatar
2 votes

Unrestricted Hartree-Fock : Density matrices initialization

When you dissociate the singlet state of H$_2$, you need the $\alpha$ and $\beta$ spatial orbitals to be different. If you use the same initial guess for both spin channels, as what happens when you ...
Susi Lehtola's user avatar
  • 19.1k
1 vote
Accepted

Computing energy and forces directly from machine learned wavefuntion/density

You can't do Hartree-Fock with densities, only. You need density matrices to evaluate exact exchange. However, you can do semilocal density functional calculations with knowledge of the electron ...
Susi Lehtola's user avatar
  • 19.1k
1 vote

Frozen core Stability Calculations in G09?

To amend the previous answers, there is no reason a priori why frozen core stability checks would not make sense. My intuition would be that the deep lying orbitals can be safely ignored in stability ...
Susi Lehtola's user avatar
  • 19.1k

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