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Exchange energy
Posted: Thu Nov 14, 2024 8:05 pm
by jiahuinie
Suppose we are using ewald potential to calculate an electron-hole fluid bilayer system, or using 1/r potential to calculate isolated 2 electron 2 hole bilayer system, how can I calculate or extract the exchange energy of the system from CASINO calculations? I noticed that in the first case CASINO will always perform a HF calculation at first, but the obtained exchange energy is not varying against the interlayer distance. I wonder is this the full exchange energy or just calculating the intralayer exchange energy against a given density?
Re: Exchange energy
Posted: Tue May 06, 2025 4:09 pm
by Neil Drummond
Particles in different layers are distinguishable, and hence there is no exchange effect between particles in different layers. Hence the Hartree-Fock energy is (correctly) independent of interlayer separation.
To calculate the interaction between electron gases in different layers, one needs to use a method such as quantum Monte Carlo that describes correlation between particles in different layers.
In an isolated biexciton system, the Hartree-Fock energy is not well defined, unless there are fixed charges. Otherwise, the biexciton simply roams freely. See my answer to your other question.
Best wishes,
Neil.
P.S. Sorry for the delay replying. For some reason I stopped receiving notifications about posts to the forum.