Inquiry About Electrostatic Potential Calculations in QUICK

[shakiralisiddiqui]

I hope this message finds you well.

I am exploring the QUICK QM Package for quantum chemistry calculations and am particularly interested in computing electrostatic potentials (like ChelPG). While the package’s Hartree-Fock and DFT capabilities seem promising, I couldn’t find explicit documentation confirming support for electrostatic potential calculations.

Could you clarify if QUICK currently supports these calculations, either directly or through post-processing of outputs like electron density or Mulliken charges? If not, are there plans to include this feature in future releases?

Thank you for your time and assistance. I greatly appreciate your work on QUICK and look forward to your response.

Best regards,
Dr. Shakir Ali Siddiqui

[agoetz]

The upcoming release of QUICK (to be labeled QUICK-25.03) will support electrostatic potential calculations. The ESP can be computed either on a grid defined by the user or a grid can be automatically generated for ESP charge fits. QUICK then also computes ESP charges.

This code is already included in AmberTools 25, where it can be used in conjunction with the antechamber tool to generate RESP charges. It is not yet documented but we can assist interested users. Any feedback on functionality and performance of our implementation would be appreciated.

An alternative option is to export a Molden file (keyword MOLDEN) and read this in with an appropriate software for post-processing (e.g. multiwfn).

[agoetz]

Adding @vtripath65 who wrote the ESP code to this discussion.

[shakiralisiddiqui]

Thanks Andrew! that is a good news. I will compile the newer version. Is there a keyword or something you might recommend to do that?

[vtripath65]

Hi @shakiralisiddiqui, you can obtain ESP charge using the keyword ESP_CHARGE. This will compute ESP charges using a spherical grid. QUICK will also generate a file containing electrostatic potential on the generated grid points. Please let me know if you have any issue.

[shakiralisiddiqui]

Hi @vtripath65 ,
Thanks, That is really helpful!
I have managed to get and install Quick-25. Yes, the ESP_CHARGE works and it generates the ESP charges. But that seem weird to me. There are some issues I am facing:

1. I have compared it with the ESP charges generated from Gaussian for exactly same geometry and ESP is totally different. Please let me know if I need to attch specific fiels or output?
2. Is there a keyword or a way to generate fitted ChelPG charges?
3. for metals as well such as Fe?

Cheers,
Shakir

[vtripath65]

Hi @shakiralisiddiqui,

It gets tricky when you start comparing results from one software to another. First of all, Gaussian uses standard orientation. Using nosymm (prevents reorienation in Guassian) might help in comparing. However, the SCF has to be converged to the same density in the two softwares for similar results. In general, the density is not exactly the same which manifests in the properties. Please try ESPGRID_SPACING = 1.0 in QUICK or some other values to see the effect. The current default is 0.25. The ESP charges converge with denser grid. You can also use different density of points in Gaussian. Iop 6/42 controls it and the default is 1 per \AA which transtates to 1 \AA spacing between points.

At present, we do not have CHELPG charges. Probably an idea for the future.

ESP charges can be obtained for the entire periodic table. However, for metals like Fe we are using the van der waals radius obtained here https://pubs.acs.org/doi/full/10.1021/acs.jctc.4c00784

Best,
Vikrant

[vtripath65]

Hi @shakiralisiddiqui,

I was wondering if you can share with me the molecule which had such different ESP charges using QUICK and Gaussian.

Thanks,
Vikrant