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PhilipW

Member

Registered: 2023-10-11

Posts: 6

Spin Density Plotting and Exchange Integral Evaluation

Hello,
For some reason when I perform coulomb and exchange integral calculations on a chromophore/radical system, the coulomb integral is nonzero (~0.04 au) but the exchange integral is always precisely zero, even when I perform the calculation on a purely quartet state. Furthermore, when I plot the spin density along a slice of the quartet state-optimzed molecule bisecting the chromophore and bridging radical, the spin density shows only nonzero density on the radical (i.e. zero ESP on the chromophore) using .molden inputs made by both ORCA and MolCAS, despite ESP showing up on a surface map visualized on Gaussian with an input cube file constructed with ORCA. Has anyone run into issues like this, or are there known bugs that might cause this?
Thanks in advance~

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,624

Website

Re: Spin Density Plotting and Exchange Integral Evaluation

Notice that exchange integral converges to zero significantly faster than Coulomb integral as overlap between the two orbitals decreases.

What does ESP mean? If it refers to electrostatic potential, note that there is no direct relationship between distribution of ESP and spin density.

PhilipW

Member

Registered: 2023-10-11

Posts: 6

Re: Spin Density Plotting and Exchange Integral Evaluation

Hello Dr. Lu,
Thank you for the reply. Apologies, I should have specified, I meant electron spin density when I say ESP.
Philip