Thanks~ I checked what you did!
It works fine!

I am glad to inform you that the function you need has been finished.
I just updated Multiwfn 3.7(dev) on Multiwfn website, in subfunction 7 of main function 6, now you can select to export electric quadrupole and octopole moment integral matrices to a text file.
In addition, subfunction 5 is newly added in main function 300, it is able to calculate electric dipole, quadrupole, octopole moments very quickly and analytically based on current density matrix and integral matrices.

Thank you so much. I will be waiting for your notice~

1 Currently it is not possible. But I will try to find time recently to implement this feature, then I will let you know here. (It is expected I can finish within one week)

2 This part of code is realized in fuzzy.f90.

I really appreciate your effort!
I have two questions. 1) is it possible to get quadrupole octupole moment matrices through Multiwfn? I have density matrices in an unusual format. so I want to read the density and operator matrix and calculate matrix multiplication with operator and get a trace of it.
2) I downloaded and check the 3.7(dev) source file but I couldn't find quadrupole/octupole moment integral functions in integral.f90 which I expect to contain the functions. Did you only upload binary files? (I didn't check binary yet)

I have updated Multiwfn 3.7(dev) on Multiwfn website. Now using subfunction 2 of main function 15, molecular dipole/quadruple/octopole moments will be outputted at the end. For example, using examples\uracil.wfn as input file, the outputted information is (all units are a.u.)

 ***** Molecular dipole and multipole moments ***** Total number of electrons: 58.000039 Molecular dipole moment (a.u.): 0.473288 1.823815 0.000736 Molecular dipole moment (Debye): 1.202978 4.635675 0.001871 Magnitude of molecular dipole moment (a.u.&Debye): 1.884225 4.789221 Molecular quadrupole moments (Standard Cartesian form): XX= -43.878912 XY= 1.812527 XZ= -0.000544 YX= 1.812527 YY= -28.230912 YZ= -0.004829 ZX= -0.000544 ZY= -0.004829 ZZ= -34.463390 Molecular quadrupole moments (Traceless Cartesian form): XX= -12.531761 XY= 2.718791 XZ= -0.000816 YX= 2.718791 YY= 10.940239 YZ= -0.007244 ZX= -0.000816 ZY= -0.007244 ZZ= 1.591522 Magnitude of the traceless quadrupole moment tensor: 13.644701 Molecular quadrupole moments (Spherical harmonic form): Q_2,0 = 1.591522 Q_2,-1= -0.008364 Q_2,1= -0.000942 Q_2,-2= 3.139390 Q_2,2 = -13.551565 Magnitude: |Q_2|= 14.001204 Molecular octopole moments (Cartesian form): XXX= 14.09463 YYY= 8.61373 ZZZ= 0.00275 XYY= 6.66406 XXY= 46.41021 XXZ= -0.00991 XZZ= 2.78071 YZZ= -7.68402 YYZ= 0.01589 XYZ= -0.00333 Molecular octopole moments (Spherical harmonic form): Q_3,0 = -0.006233 Q_3,-1= -52.517080 Q_3,1 = -5.900743 Q_3,-2= -0.012895 Q_3,2 = -0.049957 Q_3,-3= 103.261734 Q_3,3 = -4.662433 Magnitude: |Q_3|= 116.093019

You can use any input file containing GTF information for this function, for example, wfn/wfx/mwfn/fch/molden/gms. Note that the data is not calculated based on density matrix, but calculated based on the orbitals in the input file.

Yes!! I need it!!   I really appreciate for adding those features~ Can you estimate the development period for those features?

Multiwfn doesn't have a function to export electric quadrupole and octupole momentum integral matrices. If you want to calculate molecular electric quadrupole and octupole based on a given wavefunction file, I can add a new function to Multiwfn to realize this.

Hi, I'm a newbie.
In order to calculate electric quadrupole and octupole from the density matrix, I need quadrupole and octupole momentum matrices
For dipole moment, Manual (section 3.200.2) tells details but I cannot find how to build quadrupole and octupole momentum matrices.
Is it possible to build those matrices through Multiwfn?