Multiwfn forum

RGUceda

Member

Registered: 2023-05-06

Posts: 10

magnetic component of a transition

Hello good:
First of all, my sincere congratulations on your very versatile program. It's a fantastic tool.

I am interested in looking at the magnetic component of a transition. I have noticed that sometimes the transition only has a significant value on one of the axes, while sometimes both axes have significant values. Can similar structures be compared where in one case only one axis has contribution with another where two axes have?

Otherwise, and even if it could be compared, how could you make the transition that is expressed as, say 3.4 0 -2.8 become (random numbers) 5 0 0.1? In other words, it becomes significant in only one of the components

I have tried to rotate the geometry and recalculate but so far no success and still getting the same thing. I know my question is not really about Multiwfn, but I think you could help me.

Thanks a lot.

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,639

Website

Re: magnetic component of a transition

Commonly components of transition magnetic dipole moment are not of interest, and they are fully dependent of orientation. In usual quantum studies the transition magnetic dipole moment is only involved in evaluation of rotatory strength, which is independent of orientation.

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

However, I have helical molecules and the cases in which there is only one important component (for example 2.1 0.001 0), which coincides with the axis of the helix, are very illustrative. In others, due to the orientation of the molecule, there are two axes with important contributions (for example 1.8 0.003 1.5). The program asks you which component you want to get from the analysis. I would like to
have only one important component so that the images obtained are comparable (if it only has an X component, I take the projection on the X axis, etc...). A possible alternative would be to obtain the cube of the magnetic moment of the transition, without projection on any axis, but I think that this option does not exist.

Thanks again.

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,639

Website

Re: magnetic component of a transition

In subfunction 7 of main function 300 of Multiwfn, you can find an option "6 Make a vector parallel to a vector or Cartesian axis", in this option you can input a vector, and choose an axis (e.g. X-axis), then the system will be rotated so that the vector is exactly parallel to the axis, after that you can export the updated (rotated) geometry to e.g. Gaussian input file, and recalculate data based on the new geometry. Via this function, you may make transition magnetic dipole moment parallel to X-axis, and then solely analyze X-component of the moment.

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

The problem I'm seeing is that it doesn't matter what geometry I give Gaussian to do the optimization (even to calculate only the CD): the molecule rotates again and has a different geometry. It's something like Gaussian moving the reference system itself and the axes, so it doesn't matter if I change the geometry I give it. Do you know of any other tricks or ways to tell Gaussian not to make that change?

Thanks

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,639

Website

Re: magnetic component of a transition

You should add "nosymm" keyword to avoid automatic reorientation by Gaussian.

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

Hello. Thanks for your kind reply.
However, I still have a question: wouldn't it be possible to obtain the total magnetic composition, and not the component per axis? In case it can't, can't I get it somehow? I have tried to do it with cubman without success. Thanks in advance.

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

I complement what I said in the previous comment: if I reorient my molecule and recalculate I can achieve that there is only a magnetic moment in one of the components. However, I am studying lots of molecules (with also many atoms) and that would be very laborious. Bearing in mind that the program provides the X, Y and Z components, couldn't the total be obtained?

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,639

Website

Re: magnetic component of a transition

I complement what I said in the previous comment: if I reorient my molecule and recalculate I can achieve that there is only a magnetic moment in one of the components. However, I am studying lots of molecules (with also many atoms) and that would be very laborious. Bearing in mind that the program provides the X, Y and Z components, couldn't the total be obtained?

After choosing "9 Show isosurface of transition magnetic dipole moment density" in post-process menu of hole-electron analysis module, you can find an option "4: Norm, sqrt(x^2+y^2+z^2)", this corresponds to the total magnitude and it is independent of molecular orientation, is it what you need?

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

Yes, that would be just what I would want. However, option 4 does not appear for me, only options 1-3, referring to the coordinate axes. I'm using MultiWFN 3.8, so I don't understand why the option doesn't appear...

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

I just re-downloaded the program and now the option did appear. Thank you very much for your help

RGUceda

Member

Registered: 2023-05-06

Posts: 10

Re: magnetic component of a transition

Hello again
I have a new question, regarding the magnetic and electric moments of the transition. When I obtain the module of the magnetic moment with the option that you told me, everything has the same phase, which makes sense due to the definition of the option (4: Norm, sqrt(x^2+y^2+z^2) ). However, when an analogous procedure is followed for the electric momentum, the .cub shows positive and negative densities. Why this difference between one moment and another?

Thanks in advance

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,639

Website

Re: magnetic component of a transition

Hello again
I have a new question, regarding the magnetic and electric moments of the transition. When I obtain the module of the magnetic moment with the option that you told me, everything has the same phase, which makes sense due to the definition of the option (4: Norm, sqrt(x^2+y^2+z^2) ). However, when an analogous procedure is followed for the electric momentum, the .cub shows positive and negative densities. Why this difference between one moment and another?

Thanks in advance

The norm of transition electric dipole moment density was implemented with a different definition. I just updated Multiwfn on its website today, now the definition is consistent with the norm of transition magnetic dipole moment density, it is positive everywhere.