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/**********************************************************************
Smoothing_Func.c:
Smoothing_Func.c is a subroutine to calculate a smoothing function
which is used in the Krylov subspace method to smear out the
contribution of Hamiltonian and overlap matrices near the surface
of the truncated cluster.
Log of Smoothing_Func.c:
12/July/2006 Released by T.Ozaki
***********************************************************************/
#include <stdio.h>
#include <math.h>
#include "openmx_common.h"
double Smoothing_Func(double rcut,double r1)
{
double sf,a,r;
double c0,c1,c2,c3;
a = 1.0;
if (rcut<r1){
sf = 0.0;
}
else if (r1<=(rcut-a)){
sf = 1.0;
}
else{
c0 = 1.0;
c1 = 0.0;
c2 = -3.0/(a*a);
c3 = 2.0/(a*a*a);
r = r1 - (rcut - a);
sf = c3*r*r*r + c2*r*r + c0;
}
return sf;
}
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