Multiwfn forum

akramer

Member

Registered: 2026-05-19

Posts: 2

Calculating Electric Quadrupole Moments Between Excited States

Dear Dr. Tian,
Firstly, thank you for all the work you put in for producing Multiwfn, I have used many of its utilities in the past and found it very helpful! I am currently working on a project that requires the generation of electric quadrupole values between excited states similarly to how they are produced using the 18 > 5 settings for electric/magnetic dipoles (3.21.5 in the manual). Is there any way to do this with the current version of Multiwfn, and if not is there any possibility of you implementing this in the future?  I appreciate any help you can provide regarding this matter, and once again thank you for the continued development of this program.

Best,
Augusta

sobereva

Tian Lu (Multiwfn developer)

From: Athens, Greece

Registered: 2017-09-11

Posts: 2,236

Website

Re: Calculating Electric Quadrupole Moments Between Excited States

Dear Augusta,

Unfortunately it has not been implemented, and I currently do not have a clear plan to implement it because this feature is rarely used by most users.

However, it is not too difficult to modify Multiwfn source code to realize it. I can provide some clues:
The function you mentioned corresponds to "subroutine exctransdip" in excittrans.f90. As you can see, this subroutine calls "subroutine genGTFDmat" in integral.f90 to evaluate dipole moment integrals between all GTFs and store it to a matrix "GTFdipint". If you further look at "subroutine genGTFDmat", you will find it loops each pair of GTFs and calls "subroutine dodipoleint" (in integral.f90) to calculate the dipole moment integral between the GTF pairs.

To analyze transition quadrupole moment instead of the transition dipole moment, you can create a duplicate of "subroutine genGTFDmat" named e.g. "subroutine genGTFQmat" to generate e.g. "GTFQint" matrix (containing quadrupole moment integral between all GTFs), in which "subroutine domultipoleint" (already available in integral.f90) is called to calculate quadrupole integral between GTF pairs. After that, if you let "subroutine exctransdip" call "subroutine genGTFQmat" instead of "subroutine genGTFDmat" and slightly adapt a few related code lines, then transition quadrupole moment between excited states can be obtained.

Best regards,

Tian

akramer

Member

Registered: 2026-05-19

Posts: 2

Re: Calculating Electric Quadrupole Moments Between Excited States

Dear Dr. Tian,
Thank you for your kind and thorough response! I will modify the source code as you have suggested to create this utility. Once again I appreciate your fast response and your in-depth description of suggested modifications.

Best,
Augusta