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 ...
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 ...
- 10.2k
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
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 ...
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.
...
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 ...
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 ...
- 20.1k
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....
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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.
...
- 15.9k
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:
...
- 15.9k
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:
...
- 15.9k
3
votes
Accepted
Why does our PySCF-MRCC interface work for B++ but not for Li?
The answer to this question brings me back to a question I have asked before on how to handle the orbital symmetries in PySCF from UHF calculation. The following is an answer to both this and the ...
- 3,770
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 ...
- 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 ...
- 91
2
votes
FCIDUMP file from UHF calculation in PySCF
The FCIDUMP "standard" originates from Peter Knowles' full configuration interaction (FCI) program, published in Comput. Phys. Commun. 54, 75 (1989).
The orbital active space for FCI is ...
- 20.1k
1
vote
FCIDUMP file from UHF calculation in PySCF
The code for this function
For NECI, a Python function was made for writing an FCIDUMP file after a UHF calculation, and it can be found at line 308 of this file (the resulting FCIDUMP file can be ...
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