DSCF No Exchange Energy

[cwoods7]

Hello,

I am fairly new to TURBOMOLE and am trying to run a test calculation on hydrogen for HF and DFT methods. I am trying to extract the exchange energy and the coulomb energy from the dscf calculation, but it is not appearing for me. Is there any special thing I should put in the control file so that it shows me these energies? Or is there something I should look for in the output file? They seem to be present in ridft, but not in dscf. I have already done a bunch of calculations for various systems using dscf and it would be a shame if I have to re-run these calculations especially since I have the total energies anyway. Any help would be much appreciated.

[chris.hol]

Hi,

in dscf, Coulomb + Exchange energies (and matrices!) are calculated at the same time using 4-center electron repulsion integrals. Therefore, they cannot be easily separated. You can extract the combined Coulomb + Exchange energy from the "2e-ENERGY" by subtracting the exchange-correlation energy ("Exc"). If you want to further separate them, an easy workaround is to run a single ridft iteration. For this, just change "$scfiterlimit" to 1, add $rij and run ridft, preferably in a separate directory. This will then yield the converged Coulomb + exchange energies at the dscf density.

Best regards,
Christof

[cwoods7]

Thank you Christof!

I am still a little confused about the subtraction from the "2e-Energy". I have used dscf for some more complex systems and both the "Exc" and exchange terms are absent. Essentially, all I am looking for is the Coulomb energy to do a density analysis. Is there a way to just extract the coulomb energy for dscf of both HF and DFT methods? If not, I will try to run the single ridft for all of my calculations.

Best,

Cody

[chris.hol]

Hi Cody,

"Exc" and the "2e-ENERGY" should be reported in each iteration in dscf, just below the line with the iteration number. They are not reported in the end, but one can simply take the one from the last iteration. For a pure functional (without exact exchange, so non-hybrid functionals), the 2e-energy - Exc is actually the Coulomb energy. If a hybrid functional was used, no way leads around the route of using ridft for a single iteration if the Coulomb energy needs to be extracted.

An example PBE/def2-TZVP calculation on water is attached to this post. There, the 2e-energy in the last iteration is 37.577393, and Exc is -9.264745, leading to a Coulomb energy of 46.842138 Hartree.

Best,
Christof