Questions tagged [hartree-fock]

For any questions about (or related to) the Hartree-Fock method.

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6
votes
0answers
88 views

Differences between DFTB3 energy and HF energy

I was performing DFTB3 calculation with DFTB+ on water monomer. This is my input. ...
17
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3answers
1k views

Why is uncertainty not a big problem in computational chemistry?

The molecular Hamiltonian (or, for simplicity, the Fock operator) contains coulomb potentials as well as momentum operators. To evaluate the coulomb potential, we need to know where the electrons are. ...
12
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2answers
312 views

For DFT and Hartree-Fock, how can we know that we have a true minimum? Is there an equivalent to the "frequency analysis" for geometry optimization?

In a geometry optimisation, one can check if they have reached a minimum by checking the phonons. And to a certain extent, the global minimum can be confirmed by relaxing from different starting ...
7
votes
1answer
218 views

Convert reduced density matrix from M.O. to A.O. basis

I am interested in converting the one-particle reduced matrix (rdm1) from the molecular orbital (M.O.) basis to the atomic orbital (A.O.) basis. Is the following method correct (in an identical ...
8
votes
1answer
125 views

Visualize electron density using pyscf

I found the following example of code which uses density functional theory to compute the electron density $\rho$: ...
9
votes
1answer
135 views

'Exchange' in Hartree-Fock and Kohn-Sham DFT

I am a bit confused about the notions of exchange in the Hartree-Fock and Kohn-Sham Density Functional Theory schemes. In Hartree-Fock, one just writes down the many-electron wavefunction as a hartree-...
8
votes
3answers
264 views

Does Kohn-Sham DFT use Slater determinants?

In the Hartree method, it is known that the wavefunction of the system does not obey the antisymmetry principle of fermions - that is when you swap two particles, they don't up a negative sign. ...
16
votes
1answer
406 views

Why is CPHF/CPKS necessary for calculating second derivatives?

This question is coming from an answer to one of my previous questions. During optimizations, QM programs usually compute the gradient(first derivative) analytically, and take a guess of the hessian (...
12
votes
2answers
191 views

Optimization of Gaussian basis sets within the Hartree-Fock Method

I am revisiting some exercises in Thijssen's Computational Physics book, particularly chapter 4 on the Hartree-Fock method. I am interested in the method of nonlinear optimisation for its own purposes,...
6
votes
1answer
275 views

Why is my quantum chemistry software not printing as many 2e- integrals as I expect?

Background: In Hartree-Fock theory, the two-electron integral is given by: $[ij|kl]$ = $\int dx_{1}dx_{2}(\chi_{i}(x_{1})\chi_{j}(x_{1})\frac{1}{r_{12}}\chi_{k}^{*}(x_2)\chi_{l}(x_{2})$ I am ...
9
votes
2answers
257 views

Normalization constant and Roothaan Equations

Roothaan Hall Equations: The Hartree-Fock equations are a set of modified Schrodinger equations: $f_{i}\psi_{m}=\epsilon_{m}\psi_{m}$ where: The Fock operator ($f_{i}$) is given by (restricted case): ...
8
votes
1answer
183 views

Semi-canonicalisation vs canonicalisation of the Fock matrix and orbitals

I have seen the terms semi-canonicalized and canonicalized used in relation to the Fock matrix, density matrices, and orbitals; however, I am unsure what these terms actually describe. For instance: ...
9
votes
1answer
114 views

Muonic Modeling

I have seen an article[1] that describes a HF approach to working with exotic muonic atoms. I am curious about how far DFT has been extended for modeling muonic chemistry. Are there psuedopotentials ...
18
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5answers
537 views

What are the types of SCF?

Many of us know the most common types of SCF (though we can do better than Wikipedia at explaining them): RHF (Restricted Hartree-Fock), RKS (Restricted Kohn-Sham) [link to answer] UHF (Unrestricted ...
12
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1answer
167 views

Analog computing in matter modeling today: Any applications?

When we think about computers and computing today, almost invariably we think about digital computers, the ever-present objects today. But reading this question in the Chemistry stackexchange, How are ...
11
votes
1answer
320 views

How to calculate the Fock matrix in the molecular orbital basis PySCF?

I am interested in calculating the Fock matrix in the molecular orbital basis with PySCF, though I am not clear on the methodology behind this task. In my attempt, I use the following script (for the ...
12
votes
2answers
623 views

What do the rows and columns of a Fock matrix represent?

I am using the pyscf code, where the Fock matrix can be obtained by: ...
15
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2answers
476 views

Hartree-Fock density vs Kohn-Sham density

Hartree-Fock density is free of self-interaction but lacks electron correlation effects, while the density from KS-DFT (using an xc functional or potential, both which are explicitly density-dependent ...
11
votes
2answers
249 views

One-center two-electron integrals between 1s STO

As per @user1271772 's suggestion I am asking this question here again. I am trying to understand SCF cycle by trying to code up solved example from Quantum Chemistry by Levine (page 443, 5th edition)...
11
votes
2answers
162 views

What is the mathematical condition that ensure that the self-consistent field (SCF) procedure must converge?

We know that there is convergence issue of DFT method on study real molecular system. It would be conducive if people could pre-determine if the SCF procedure is converge analytically before starting ...
15
votes
2answers
503 views

How does the Hartree-Fock method improve on Hartree after considering the wavefunction that takes the anti-symmetry property into account?

I am not able to understand the math of this. After taking the Slater determinant as a wavefunction in Hartree-Fock, does the procedure to find wavefunctions remain the same as in the Hartree method ...