Multiwfn forum

smaity

Member

Registered: 2025-07-11

Posts: 3

Transition Dipole Moment from TrESP Charges

Dear Tian,

Thank you very much for developing and maintaining such a great program. Multiwfn’s ability to work with many different quantum chemistry packages is really impressive.

I noticed something unusual when using TrESP charges from quantum chemistry software like Gaussian or ORCA, followed by transition density analysis in Multiwfn. The transition dipole calculated by projecting the charges onto atomic positions seems to point in a different direction compared to the transition dipole moment vector reported by the quantum chemistry software.

I understand the direction of the transition dipole can be arbitrary due to phase conventions, but since both results are based on the same wavefunction, I expected consistency. It seems there may be a sign mismatch in how Multiwfn interprets the transition density compared to the original quantum chemistry software.

Thanks.

Best regards,
Sayan

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 2,015

Website

Re: Transition Dipole Moment from TrESP Charges

Dear Sayan,

I have checked, but didn't find this problem, there is no sign convention issue in the current implementation. Perhaps the equation you used to evaluate transition dipole moment based on TrESP is incorrect. The correct code should like as follows:

    xdip=0
    ydip=0
    zdip=0
    do iatm=1,ncenter
        xdip=xdip+a(iatm)%x*a(iatm)%charge
        ydip=ydip+a(iatm)%y*a(iatm)%charge
        zdip=zdip+a(iatm)%z*a(iatm)%charge
    end do
    write(*,*)
    write(*,"(' Dipole moment (a.u.): ',3f14.6)") xdip,ydip,zdip

where a%charge directly corresponds to the TrESP charges given by Multiwfn, and no additional negative sign should be included.

Best regards,

Tian

smaity

Member

Registered: 2025-07-11

Posts: 3

Re: Transition Dipole Moment from TrESP Charges

Dear Tian,
I calculated the TrESP charges using Multiwfn after performing TD-DFT calculations in ORCA. When I load the .chg file, I am getting,

Sum of all atomic charges:   -0.000001
Component of electric dipole moment:
X=   -3.400656 a.u.  (   -8.643605 Debye )
Y=   -0.813395 a.u.  (   -2.067445 Debye )
Z=   -0.189457 a.u.  (   -0.481550 Debye )
Total electric dipole moment:    3.501709 a.u.  (    8.900457 Debye )

but within the ORCA, it is printed  as:

-----------------------------------------------------------------------------
         ABSORPTION SPECTRUM VIA TRANSITION ELECTRIC DIPOLE MOMENTS
-----------------------------------------------------------------------------
State   Energy    Wavelength  fosc         T2        TX        TY        TZ
        (cm-1)      (nm)                 (au**2)    (au)      (au)      (au)
-----------------------------------------------------------------------------
   1   16212.1    616.8   0.608305451  12.35258   3.41287   0.81815   0.18857

Clearly, the transition dipole signs from Multiwfn and ORCA do not match. The same issue when I use Gaussian also. Hope you understand the question.
Best,
Sayan

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 2,015

Website

Re: Transition Dipole Moment from TrESP Charges

Dear Sayan,

I am not sure if your TrESP charges have been correctly generated. Just taking the example in Section 4.A.9 of Multiwfn manual, S0-S0 transition of 4-nitroaniline. By following the step in the manual (I'm using Gaussian 16), you should have .chg file with following content:

C    -0.003279    0.022698    1.208952   0.2134106035
C    -0.003279   -1.356850    1.208468  -0.1679471876
C    -0.002220   -2.074407    0.000000   0.1841565861
C    -0.003279   -1.356850   -1.208468  -0.1681325143
C    -0.003279    0.022698   -1.208952   0.2136075560
C    -0.002956    0.708053    0.000000  -0.1725671768
H    -0.002297    0.584212    2.134941  -0.0164467259
H    -0.008330   -1.894941    2.152080   0.0062724543
H    -0.008330   -1.894941   -2.152080   0.0063059790
H    -0.002297    0.584212   -2.134941  -0.0165045142
N    -0.047761   -3.443794    0.000000   0.1716754368
H     0.214094   -3.921723    0.844971   0.0002801698
H     0.214094   -3.921723   -0.844971   0.0003282958
N     0.000588    2.162345    0.000000  -0.0646299850
O     0.002065    2.727687   -1.077690  -0.0949102566
O     0.002065    2.727687    1.077690  -0.0948987209

If you load this file into Multiwfn, you will see

 Component of electric dipole moment:
 X=   -0.016488 a.u.  (   -0.041908 Debye )
 Y=   -2.518398 a.u.  (   -6.401129 Debye )
 Z=    0.000017 a.u.  (    0.000043 Debye )
 Total electric dipole moment:    2.518452 a.u.  (    6.401267 Debye )

As mentioned in Multiwfn manual, the TrESP calculated based on Gaussian .wfn file should be divided by sqrt(2), and thus the transition dipole moment should also be fixed in this way. So, for example, Y component of transition dipole moment of S0-S2 should be -2.518398/sqrt(2)=-1.78077 a.u.

Now, look at Gaussian output file (4-Nitroaniline_IOp.out in the TrEsp.zip), you can find

 Ground to excited state transition electric dipole moments (Au):
       state          X           Y           Z        Dip. S.      Osc.
         1        -0.0000     -0.0000      0.0001      0.0000      0.0000
         2        -0.0165     -1.7911      0.0000      3.2083      0.3408
         3         0.0210      0.0188      0.0000      0.0008      0.0001

Clearly, the corresponding data is -1.7911, which is very close to the -1.78077 calculated based on TrESP. So, there should be no sign issue.

As you are an ORCA user, I would like to note that if you are using TDDFT, currently Multiwfn is unable to accurately calculate TrESP, since ORCA doesn't print excitation and de-excitation configuration coefficients separately. You have to use TDA-DFT instead. (PS: The situation will be changed in the next release ORCA).

Best,

Tian