1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
|
subroutine exchpt(d,s,u,v,vx)
c gga91 exchange potential for a spin-unpolarized electronic system
c input d : density
c input s : abs(grad d)/(2*kf*d)
c input u : (grad d)*grad(abs(grad d))/(d**2 * (2*kf)**3)
c input v : (laplacian d)/(d*(2*kf)**2)
c output vx : exchange potential per electron
implicit double precision (a-h,o-z)
data a1,a2,a3,a4/0.19645d0,0.27430d0,0.15084d0,100.d0/
data ax,a,b1/-0.7385588d0,7.7956d0,0.004d0/
data thrd,thrd4/0.333333333333d0,1.33333333333d0/
fac = ax*d**thrd
s2 = s*s
s3 = s2*s
s4 = s2*s2
p0 = 1.d0/dsqrt(1.d0+a*a*s2)
p1 = dlog(a*s+1.d0/p0)
p2 = dexp(-a4*s2)
p3 = 1.d0/(1.d0+a1*s*p1+b1*s4)
p4 = 1.d0+a1*s*p1+(a2-a3*p2)*s2
f = p3*p4
p5 = b1*s2-(a2-a3*p2)
p6 = a1*s*(p1+a*s*p0)
p7 = 2.d0*(a2-a3*p2)+2.d0*a3*a4*s2*p2-4.d0*b1*s2*f
fs = p3*(p3*p5*p6+p7)
p8 = 2.d0*s*(b1-a3*a4*p2)
p9 = a1*p1+a*a1*s*p0*(3.d0-a*a*s2*p0*p0)
p10 = 4.d0*a3*a4*s*p2*(2.d0-a4*s2)-8.d0*b1*s*f-4.d0*b1*s3*fs
p11 = -p3*p3*(a1*p1+a*a1*s*p0+4.d0*b1*s3)
fss = p3*p3*(p5*p9+p6*p8)+2.d0*p3*p5*p6*p11+p3*p10+p7*p11
vx = fac*(thrd4*f-(u-thrd4*s3)*fss-v*fs)
return
end
|
