# Questions tagged [hartree-fock]

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

70 questions
Filter by
Sorted by
Tagged with
88 views

### At what point in the Hartree-Fock formalism is the Fock operator introduced?

I seem to be having a conceptual problem with HF theory as to where the Fock operator comes from. In order to explain the context of my conceptual problem, I will include how HF was derived according ...
• 397
61 views

### CCSD calculation between two orbitals

I am trying to calculate the CCSD energies between two orbitals. Suppose I have a system, ...
• 1,024
70 views

### Computing energy and forces directly from machine learned wavefuntion/density

I have been reading up on methods where electron density was estimated directly from some machine learning method, followed by evaluation of energy and forces[1,2]. My understanding is that this is ...
• 545
172 views

• 165
66 views

### How to choose the orientation of basis functions in a Gaussian calculation?

I am trying to run a g09 calculation for a D5h symmetric molecule using the HF/LANL2DZ level of theory. The molecule is pentagonal planar in geometry, and I would like to visualize the canonical ...
• 397
211 views

### Time Evolution of the Hartree-Fock Wave Function

The Hartree-Fock Hamiltonian is given by $$\hat{H} = \sum_i \hat{h}_i + \frac{1}{2}\sum_i\sum_j \left[\hat{J}_{ij} - \hat{K}_{ij}\right]$$ and by choosing a basis, the Hamiltonian can be written in ...
• 187
264 views

### Frozen core Stability Calculations in G09?

I am trying to calculate the stability of CO at HF/3-21g level using G09. I am trying to reproduce an issue that was observed in PySCF, and I have made the following observations: If I use the ...
• 3,997
185 views

### Calculate the energy of a single electron in an atom

When we employ Hartree-Fock or coupled cluster to calculate an atom's energy, can we directly obtain the valence electron energy? Is it as simple as looking at the orbital energy? I know that summing ...
• 187
145 views

### Electronic Structure Calculation with External Field

There are various programs for calculating energy states for molecules (ORCA, Gaussian, ...). Is there also software that allows the same simulations with an additional external potential (e.g. ...
97 views

### Molecular integrals in spherical harmonics?

I have been trying to write a basic HF code that can compute the MOs and total energy of a molecule. I followed the following reference for overlap and kinetic integrals. During a conversation with a ...
• 3,997
1 vote
112 views

### Hartree Fock method

Currently, I'm studying (again from zero and more in detail) Hartree Fock (HF) method, specifically the Restricted Hartree Fock (RHF). I'm following two books: "Introduction to Computational ...
• 165
161 views

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

The Broyden (BroydenāFletcherāGoldfarbāShanno or BFGS) algorithm can be known in the matter modeling to optimize a crystal lattice geometry ā to clarify positions of nodes of a crystal lattice in ...
• 967
860 views

### Free and optimized code for Hartree-Fock calculation in solids

I am looking for a free code for Hartree-Fock calculations in solids especially a code optimized (quite fast) compared to Pyscf which is quite slow and unstable. I do not have any clue to explain why ...
• 916
159 views

### Can specifications of a second-order phase transition of a solid be obtained with the Hartree-Fock (or DFT) calculation?

At some temperature a crystal lattice of a solid can be rearranged or to say it more precise - got new positions of its cores. This phenomenon is well-known to be called a second-order phase ...
• 967
1k views

### Numerical Evaluation of Hessian?

I am trying to understand the construction of Hessian matrix using numerical differentiation (NUMFREQ option in ORCA for example). I understand that Hessian is a square matrix containing second ...
• 3,997
656 views

### How to use libint with Python

I am trying to write a basic Hartree-Fock code to compute orbital energies and total energy of a molecule at almost all basis sets. I wrote the integral code in Cython/Python and is very slow. I would ...
• 3,997
424 views

### How is the zero energy defined for molecular orbitals?

In DFT and Hartree-Fock bonding orbitals have negative energies while antibonding orbitals have positive energies. Why is this the case? It seems this is due to the zero-point energy being defined for ...
• 391
299 views

### Effective core potential (ECP) calculations

I'm setting up a simple Hartree-Fock problem in pyscf with ECPs to test things out. However, the numbers I get do not make sense to me as the energies are very different. I have never used ECPs before ...
• 163
289 views

### How to evaluate Hartree--Fock exchange energy density on grids in pyscf?

I am trying to evaluate the Hartree--Fock exchange energy density on grids in pyscf with an instance of class "UKS", in order to test some functionals depending on the exchange energy ...
• 123
53 views

### How to calculate the forces of attraction between a surface and molecules of a substance at a corrosion affection? [closed]

Previously, a question was asked about an equation that is able to calculate the forces of attraction between a surface and molecules (of another substance). During the discussion of the question a ...
• 967
1k views

### Is there a simple free working code that implements HartreeāFock or DFT?

Is there somewhere in the internet a good simple free working code (with a minimal number of lines in its presentation) that implements a calculation of eigenvalues with HartreeāFock (or DFT) ...
• 967
954 views

### How to detect an "open shell" molecule?

I feel like this is a really stupid question, and I've been ashamed to ask for a while... When I'm about to run some electronic structure calculation on a molecule, how do I know if I need to use an ...
350 views

### Hartree Fock Algorithm too high values for Molecules

I am working on a high school graduation paper on Hartree Fock and have gotten pretty far already. With help from this community, I managed to generate all the necessary integrals and implement the ...
• 125
127 views

### Implementation of one-elecron integrals in a Hartree-Fock program

Absolute newbie in quantum chemistry here. I was recently looking through some Fortran libraries from my university to see if I understand all of the mathematics. In a Hartree-Fock library, I found ...
• 53
532 views

### How to read two electron integrals from pyscf [closed]

This is a follow-up question to this one I asked a few days ago. I in the meantime talked to my teacher and generate all the necessary integrals in PySCF. For the one electron integrals that isn't an ...
• 125
195 views

### What is the best algorithm for ERIs of contracted gaussian atomic orbitals

I am currently working on python script that does Hartree-Fock-Calculations. I try to avoid packages as good as possible. I've figured out how to calculate the one electron integrals when it comes to ...
• 125
734 views

### What is the physical meaning of the term "non-local interaction"?

This term pops up through out Hartree-Fock and DFT. Does this term have any physical significance to actual(real) system or it is a mathematical by-product?
• 363
241 views

### Continuously-varying Hartree-Fock transition matrix?

Suppose we have a parametrized molecular Hamiltonian $H(R)$, where $R$ are the nuclear coordinates. If we let $B(R)$ be some chosen atomic basis set (like STO-3G) centred at $R$, then using $B(R)$, we ...
• 409
682 views

### Molecular orbital values on grid points in PySCF?

I am looking for a way to easily evaluate individual molecular orbitals on a grid(assuming a single determinant method for now) in PySCF. I am aware on how to generate efficient grids for real-space ...
• 624
132 views

### Is it possible to obtain the current-voltage characteristic for a crystal using the HartreeāFock (or DFT) calculation? [closed]

In continuation of the question of obtaining an electrical conductivity tensor (ECT) from the āfirst characteristicsā, will my following suggestion be correct? Since a crystal with an applied-to-it ...
• 967
235 views

### Simple question about Hartree-Fock algorithm

Classically in Hartree-Fock implementations we define the wave-function in term of a basis set: $$\phi_i = \sum_{\alpha} C_{\alpha i}\chi_\alpha$$ If I understand correctly the problem is reduced to ...
• 1,417
129 views

### Can the electrical conductivity tensor of a crystal be obtained from a Hartree-Fock calculation?

Letās assume that a crystal has been calculated by HartreeāFock (HF) method (or DFT one), i.d., so to speak, the "first characteristics", which are eigenvalues and eigenvectors, as well as ...
• 967
192 views

### In which part of the HartreeāFock algorithm (or DFT one) could a neural network be most effectively used?

I understand that the task of implementing machine learning in DFT and HartreeāFock (HF) algorithm has already been solved, perhaps to some extent, but it is interesting to think about how to ...
• 967
94 views

### Rys Quadrature method for integrating over Gaussian basis functions: 1D integral recursion relation [closed]

I'm trying to implement the Rys Quadrature method for integrations of Gaussians, from scratch. I'm using this paper as a reference. So, how does the overall recursion relation for evaluating 1D ...
614 views

### Which formalism is better suited to model a crystal with defects: HartreeāFock, KohnāSham, or something else?

Letās suppose that (1) itās required to calculate a crystal with certain parameters of a crystal lattice; (2) this crystal has some defects (let it be Frenkel defects for simplicity); (3) these ...
• 967
304 views

### Hartree-Fock Method: Projection of density matrix onto a larger basis set

I am implementing a Hartree-Fock SCF program with an educational purpose. Although the code works fine using a Core Hamiltonian guess for the SCF iterative process, I want to implement a more accurate ...
• 153
95 views

### About the order of indices in basis set expansion

In many books, e.g., Szabo and Ostlund, Helgaker Jorgensen and Olsen, etc etc, the expansion of Hartree-Fock orbital by basis set is written as a kind of $$\phi_i = \sum_{\mu} C_{\mu i} \chi_{\mu}$$ ...
2k views

### What are the physical reasons if the SCF doesn't converge?

I've been mostly using ab initio methods as a routine calculation tool, so even though I know some things from the theoretical side, I still have mostly hands-on experience. One of the things that I ...
356 views

• 605
153 views

### How to read data from an input and form two-electrons integral?

I am doing a code that can calculate the hartree-fock energy. I want to form the two-electrons integral by reading the data from the input like this one below. The first four number are the indices ...
• 1,512