# Questions tagged [integrals]

For 1- and 2-electron integrals in electronic structure calculations, before Hartree-Fock or some other type of self-consistent-field calculation, or the integral transformation which is done after HF or SCF.

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### Reintegrate calculation results from ORCA using finer grid?

I have made a bunch of calculations in ORCA to compare them to results from this paper. The original calculations from this paper were done in TurboMole. I tried to recreate the method as best I could ...
44 views

### Correct expressions for one-center Gaussian radial two-electron integrals

I am working on a new atomic solver library, for which I need expressions for the one-center two-electron integrals. Pitzer has furnished the necessary expressions for Slater-type and Gaussian-type ...
122 views

### How are 2-electron integrals usually computed?

I want to compute 2-electron coulomb integrals. When the Primitive Gaussian is not centered at 0, my quadrature scheme fails unless I increase the number of quadrature points. I am currently using a ...
81 views

### Analytical derivative of nuclear-electron attraction integrals over gaussian functions

I'm currently writing a program which evaluates the first derivatives of molecular integrals (over gaussian basis sets) with respect to the cartesian coordinates of the nucleus. I'm somewhat stuck ...
25 views

### PySCF two-electron integrals between two fragments

I am trying to compute integrals of the form $(pq|rs)$ where the orbitals $p$ and $q$ are orthogonalized atomic orbitals for a fragment $A$ and $r,s$ are orthogonalized on fragment $B$. I was thinking ...
339 views

### Does PySCF use chemist's or physicist's notation for 1- and 2-electron integrals?

I am trying to evaluate 1- and 2-electron integrals using PySCF trough this code: Hij = mol.intor('int1e_kin') + mol.intor('int1e_nuc') Vijkl = mol.intor('int2e') ...
262 views

### PySCF: 2-index and 3-index matrix

The 4-index 2-electron integral can be obtained for the He atom with the following code: ...
223 views

### Becke partitioning : Computing integrals with Lebedev and Gauss-Chebyshev quadrature

Preface: This question is a follow up post from a previous question on MMSE: Usual way of computing exchange-correlation potential on a simple case H2 (RHF, LDA). The radial variable substitution and ...
75 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 ...
42 views

### How can I get 2c2e and 3c2e integrals using the erf kernel in PySCF? [closed]

I want to reproduce the calculation procedure of density fitting in PySCF. I know how to get the 2c2e/3c2e integrals matrix/tensor with $1/r_{12}$ kernel by using ...
1 vote
270 views

### PySCF: How to do CCSD calculations from an FCIDUMP file in HDF5 format?

Recently my question: Why does CCSD work, but not CCSD(T), after reading an FCIDUMP in PySCF? lead to a bug fix that allows users to do CCSD(T) calculations from an FCIDUMP file in PySCF. That was ...
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### Interacting with pyscf integral library from Fortran [closed]

I would like to use libcint, the integral library in pyscf from Fortran. Its webpage has a Fortran API and developer manual, but ...
292 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 ...
948 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 ...
140 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 ...
118 views

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### 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 ...
398 views

### How do the various programs read or write integrals in FCIDUMP format?

The FCIDUMP format was created by Peter Knowles and Nick Handy circa 1989 and now allows many electronic structure software packages to interact with each other. ...
508 views

### What programs can do electron integrals and SCF calculations with more than one CPU?

Similar to this question which asks for each answer to provide one software that can do CASSCF: I am interested in software that can do integrals, SCF (Hartree-Fock), and the integral transformation, ...
1k views

### Which software is good with generally contracted basis sets?

Recently, I learnt that basis sets can be contracted as segmented (like def2 or 6-31G) or general (like cc-PVTZ, or ANO). The general contraction allows all the primitives to appear in all shells, ...
203 views

### For software that does not support FCIDUMP format, what format is used and how can we get the software to interact with FCIDUMP integrals?

Complementary to this question: How do the various programs read or write integrals in FCIDUMP format? which attempts to list all electronic structure packages that support the ...
559 views

### What do the indices mean in an FCIDUMP file?

I generated an FCIDUMP file, which is copied below ...
355 views

### Exchange-Correlation Two-Electron Integrals

Do any freely available or proprietary electronic structure packages explicitly compute two-electron exchange correlation integrals? I have found a few derivations to calculate excited state ...