From 5df79c53745fde5d6c3340a2979b1429cd5892c1 Mon Sep 17 00:00:00 2001 From: Henrik Rydberg Date: Sat, 8 Oct 2011 20:30:28 +0200 Subject: Initial import of htcd system 1.0 Signed-off-by: Henrik Rydberg --- src/labat/exchen.f | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) create mode 100644 src/labat/exchen.f (limited to 'src/labat/exchen.f') diff --git a/src/labat/exchen.f b/src/labat/exchen.f new file mode 100644 index 0000000..a3d1112 --- /dev/null +++ b/src/labat/exchen.f @@ -0,0 +1,21 @@ + subroutine exchen(d,s,ex) +c gga91 exchange energy for a spin-unpolarized electronic system +c input d : density +c input s : abs(grad d)/(2*kf*d) +c output ex : exchange energy 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/0.333333333333d0/ + fac = ax*d**thrd + s2 = s*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 + ex = fac*f + return + end -- cgit v1.2.3