| 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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