Questions tagged [hartree-fock]

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

Filter by
Sorted by
Tagged with
4 votes
0 answers
60 views

CCSD calculation between two orbitals

I am trying to calculate the CCSD energies between two orbitals. Suppose I have a system, ...
6 votes
2 answers
145 views

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

I recently wrote a simple HF SCF program for my understanding and realized that I do not fully understand such QM calculations. Suppose I have the ground state gaussian wave function of a system, $$ \...
4 votes
1 answer
66 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 ...
4 votes
2 answers
139 views

Post-hartree fock calculation with localized Molecular orbitals in PySCF

I have localized the canonical Hartree-Fock orbitals for a molecule in PySCF. Now I want to perform ccsd calculations with these localized orbitals. Is it possible with pyscf? Example with CCSD with ...
4 votes
1 answer
99 views

Unrestricted Hartree-Fock : Density matrices initialization

I have some results about the energy of H2 as a function of the bond length using Restricted HF (RHF) and Unrestricted HF (UHF) methods. With a zero-initialization of the density matrix I have the ...
4 votes
1 answer
301 views

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

I have been using PySCF to calculate the 1-particle and 2-particle density matrix from ccsd(T) wavefunction using these modules in-built in PySCF make_rdm1() and <...
5 votes
2 answers
109 views

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

Does anyone know of a paper, textbook, or other resource which outlines the expression for the analytic gradient of the HF energy (restricted or otherwise) in terms of Dunning's contracted Gaussian-...
1 vote
0 answers
65 views

Factorization of a closed shell Slater determinant into spatial and spin part

I'm studying the HF method, so I have a non-relativistic time-independent Hamiltonian. Since in the Hamiltonian, there is no spin, we have: $$ \left[\hat{H}, \hat{S}_z \right] = 0 \quad \text{and} \...
3 votes
0 answers
63 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 ...
3 votes
2 answers
181 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 ...
10 votes
1 answer
202 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 ...
6 votes
3 answers
251 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 votes
0 answers
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. ...
9 votes
2 answers
650 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?
5 votes
0 answers
144 views

Locating Symmetry Equivalent Atoms from Distance Matrix?

As a follow up to my previous question here, I am now trying to implement symmetry detection in my code. I am following the paper by Beruski et. al to understand the background required. I am able to ...
3 votes
1 answer
90 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 ...
1 vote
0 answers
110 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 ...
5 votes
1 answer
160 views

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

The Broyden (Broyden—Fletcher—Goldfarb—Shanno or BFGS) algorithm can be known in the matter modeling to optimize a crystal lattice geometry — to clarify positions of nodes of a crystal lattice in ...
10 votes
2 answers
831 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 ...
5 votes
1 answer
154 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 ...
3 votes
1 answer
129 views

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

Let’s assume that a crystal has been calculated by Hartree–Fock (HF) method (or DFT one), i.d., so to speak, the "first characteristics", which are eigenvalues and eigenvectors, as well as ...
5 votes
1 answer
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 ...
4 votes
2 answers
641 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 ...
15 votes
3 answers
1k views

Is there a simple free working code that implements Hartree–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 Hartree–Fock (or DFT) ...
7 votes
1 answer
388 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 ...
6 votes
1 answer
289 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 ...
5 votes
2 answers
265 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 ...
5 votes
1 answer
190 views

In which part of the Hartree–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 Hartree–Fock (HF) algorithm has already been solved, perhaps to some extent, but it is interesting to think about how to ...
2 votes
0 answers
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 ...
8 votes
1 answer
851 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 ...
5 votes
1 answer
333 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 ...
5 votes
1 answer
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 ...
2 votes
0 answers
459 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 ...
5 votes
1 answer
183 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 ...
4 votes
1 answer
602 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 ...
6 votes
1 answer
239 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 ...
7 votes
2 answers
227 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 ...
4 votes
0 answers
128 views

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

In continuation of the question of obtaining an electrical conductivity tensor (ECT) from the “first characteristics”, will my following suggestion be correct? Since a crystal with an applied-to-it ...
5 votes
2 answers
611 views

Which formalism is better suited to model a crystal with defects: Hartree–Fock, Kohn–Sham, or something else?

Let’s suppose that (1) it’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 ...
4 votes
0 answers
93 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 ...
10 votes
2 answers
2k views

Visualize electron density using pyscf

I found the following example of code which uses density functional theory to compute the electron density $\rho$: ...
7 votes
1 answer
285 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 ...
5 votes
1 answer
93 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 $$ \phi_i = \sum_{\mu} C_{\mu i} \chi_{\mu} $$ ...
19 votes
4 answers
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 ...
7 votes
0 answers
334 views

Evaluating Coulomb and exchange integrals in practice using cartesian coordinates [closed]

Many software packages provide means to calculate the Coulomb and exchange integrals, for example, the exchange $$\int \phi^*(1) \, \psi^*(2) \frac{1}{|\mathbf{r_1} - \mathbf{r_2}|} \, \psi(1) \, \phi(...
8 votes
0 answers
98 views

Is the formula of a Dyson orbital independent of whether there is degeneracy or not in the HOMO of the neutral?

A Dyson orbital is defined as: $$ \textrm{Dy}(x) = \int dx_1 \ldots dx_{N-1} \, (\Psi^+(x_1,\ldots,x_{N-1}))^* \, \Psi^0(x_1,\ldots,x_{N-1}, x),\tag{1} $$ where $\Psi^0$ and $\Psi^+$ are the total ...
7 votes
1 answer
358 views

Exploiting 8-fold symmetry of ERI tensor for building Coulomb and Exchange matrices

I'm trying to write a restricted Hartree Fock code in Fortran that reads in a file of zeroth-iteration 1 and 2 electron integrals (FCIDUMP format) and uses them to do the SCF procedure from an initial ...
8 votes
1 answer
926 views

What do size-extensivity and size-consistency mean?

I have heard both terms in various lectures and books on quantum chemistry, however, I have not found a proper explanation of them. As I understand now, size consistency of a method means for example, ...
6 votes
1 answer
1k views

How to compute the overlap matrix in Python

I want to calculate the overlap integral (S), I made the code, but it is only worked when I use a basis function that describe 1s and when I include 2s orbital, I start to get error. The First Problem ...
8 votes
1 answer
149 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 ...