Skip to main content
11 votes
Accepted

How to calculate FCI matrix elements from an FCIDUMP file

Let's go back to the original paper where the fcidump format was first proposed: A determinant based full configuration interaction program by Peter Knowles (lead author of the MOLPRO program, along ...
Nike Dattani - No Free Time's user avatar
6 votes
Accepted

What do the parameters at the top of an FCIDUMP file mean?

MS2 is related to the spin. Specifically, it is the number of unpaired electrons. Your molecule is a singlet, which is why it says ...
Nike Dattani - No Free Time's user avatar
6 votes

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

MRCC MRCC stores 1- and 2-electron integrals in an ASCII file called fort.55 which is formatted very similarly to FCIDUMP. The <...
6 votes

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

AFAIK the standard way is to obtain the memory efficiency at the expense of some code repetition in the innermost loop. A preliminary example goes like: Construct a nested loop that only loops over ...
wzkchem5's user avatar
  • 9,670
5 votes
Accepted

Using the same input (MINP) file, why does MRCC fail with a "normal" fort.55 file, but succeeds with a longer fort.55 file that has duplicate entries?

The good news I got MRCC working properly with your first fort.55 file, by a very small modification of your MINP file. ...
Nike Dattani - No Free Time's user avatar
5 votes

What do the indices mean in an FCIDUMP file?

"I was able to guess most of results, except the ones with value 0.663472." I am able to confirm that your integrals are correct even for the 0.663472 case, because by calculating them ...
Nike Dattani - No Free Time's user avatar
5 votes

How are one-/two- particle reduced density matrices printed in mainstream programs?

1RDMs are just simple matrices, which can be stored in either dense or sparse form, possibly combined with triangular storage (the matrix is often symmetric). 1RDMs are passed around in a number of ...
Susi Lehtola's user avatar
  • 19.7k
4 votes

What do the indices mean in an FCIDUMP file?

I would like to post a partial answer that I have for now. For the indices ijkl in the FCIDUMP file, it corresponds to the integral (see https://theochem.github.io/horton/2.0.2/user_hamiltonian_io....
fagd's user avatar
  • 231
3 votes
Accepted

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

Thanks for all these troubleshooting. As you noticed, ao2mo.kernel does not give "an FCIDUMP file in HDF5 format", but only provides 2-electron integrals ...
X. Wang's user avatar
  • 91
3 votes
Accepted

Why does CCSD work, but not CCSD(T), after reading an FCIDUMP in PySCF?

FCIDUMP only contains limited information about the system (e.g. numbers of orbitals and electrons, spatial symmetries of orbitals, etc.) and 1- and 2-electron integrals in MO basis. The FCIDUMP ...
X. Wang's user avatar
  • 91
3 votes
Accepted

How to compute the overlap matrix in Python

Here is an updated version of your code that I believe now works. I had to add in a few of the values that were computed elsewhere in your code, but otherwise it is mostly the same. ...
Tyberius's user avatar
  • 15.6k
3 votes
Accepted

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

I'm not sure how your current code is supposed to work. Focusing just on the first half: ...
Tyberius's user avatar
  • 15.6k
3 votes

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

GAMESS(US) has this facility implemented, but this feature may not be available in the public release.
Dipayan Datta's user avatar
3 votes

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

Psi4 Psi4 provides functions for reading and writing FCIDUMP files from wavefunction objects. Using Psi4 as a Python module, these look something like: ...
Tyberius's user avatar
  • 15.6k

Only top scored, non community-wiki answers of a minimum length are eligible