From NWChem
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Just Got Here
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| 9:31:50 AM PDT - Thu, Aug 29th 2013 |
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In the current documentation, it says that LC-PBE0 (also called CAM-PBE0) is requested by specifying:
xc xcampbe96 1.0 cpbe96 1.0 HFexch 1.0
cam 0.30 cam_alpha 0.25 cam_beta 0.75
which I interpret as alpha=25% short-range HF exchange, varying with an error function (scaling=cam) to alpha+beta=100% HFexch at long range. Conversely, we have 1-alpha =75% campbe96 exchange at short range, being damped to 1-(alpha+beta)=0% at long range range. The "1.0" after xcampbe96 and HFexch, I interpret as "global" scaling factors.
Now, to request LC-wPBEh, one should specfiy:
xc xwpbe 0.80 cpbe96 1.0 hfexch 1.00
cam 0.2 cam_alpha 0.20 cam_beta 0.80
And, here, I do not understand the first line. Why the 0.80 after xwpbe? If I have to take care that alpha and the (global?) scaling factor of xwpbe add up to 1.0, why is this not the case for CAM-PBE0? Does that mean I have 125% exchange in CAM-PBE0? Or does it mean that I have just 0.8*(1-alpha) short-range wpbe in LC-wPBEh? Or do the two short-range GGA exchange philosophies require fundamentally different input specification?
I would be very much obliged if someone could help me out in my limited understanding here.
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Niri Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Forum Regular
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Posts 187
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| 3:40:49 PM PDT - Wed, Sep 11th 2013 |
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Hi,
I see your confusion. For the LC-PBE0 (or CAM-PBE0), The xcampbe96 functional is the LC or CAM modified short-range DFT (PBE exchange). We actually scale this by (1-alpha-beta*erf) in the code so that the total amount of exchange in the short and long-range are 1.0
We do the LC-wPBEh functional a bit differently. The scale factor is directly used from the first line.
Best,
-Niri
niri.govind@pnl.gov
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