Author Topic: optB88 density functional in QATK  (Read 208 times)

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Offline Ángel D.

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optB88 density functional in QATK
« on: April 10, 2022, 00:56 »
Hello, QATK community!
I hope I haven't posted on the wrong place. I was comparing some QATK capabilities on a MoS_2 bilayer system, trying to take into account van der Waals forces in order to predict some layer properties. Following many references, I wanted to try optB88. According to the reference given in QATK manual, its exchange part has one parameter, so I guess the corresponding exchange functional is OneparameterB88, right? What about the correlation part? If I'm right, it consists of a local LDA part and a nonlocal part (the most important for vdW in this case, I guess). I noticed there's an available correlation functional named Becke88DionVanDerWaals, but I don't think that's the good one, because it cannot reach convergence (9x9x1 k points and 55 H density-mesh cutoff). Which one would make the famous complete optB88?
Thanks in advance!
« Last Edit: April 11, 2022, 11:12 by Ángel D. »

Offline Anders Blom

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Re: optB88 density functional in QATK
« Reply #1 on: June 7, 2022, 07:58 »
Nomenclature for XC functionals is a quagmire...! I hope I am right in this, but I believe optB88 is just an exchange functional and has itself no vdW in it. There is a version, or combination, referred to as optB88-vdW as used e.g. in https://www.mdpi.com/2073-4352/9/7/348/pdf (with PBE as correlation) but as far as I know, that requires that vdW is implemented separately in the functional. This is currently not available in QuantumATK, but I hope we can include it in the future.

Offline Ángel D.

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Re: optB88 density functional in QATK
« Reply #2 on: June 10, 2022, 21:48 »
Thank you very much for your answer, sir!