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#include <stdio.h>
/*****************************************************************
Improved analytical tetrahedron method
Idea: PRB 49, 16223 (1994), by Bloechl, Jepsen and Andersen
*******************************************************************/
/*
input e[0:3],n
output: e[0]<e[1]<e[2]<e[4]
*/
void OrderE0(double *e, int n)
{
int i,j;
double t;
for (i=0;i<n-1;i++) {
for (j=i;j<n;j++) {
if (e[j]<e[i]) {
t = e[j];
e[j]=e[i];
e[i]=t;
}
}
}
}
/*
input e[0:3],a[0:3],n
output: e[0]<e[1]<e[2]<e[4]
a[] is also interchanged corresponding to e[]:
*/
void OrderE(double *e,double *a, int n)
{
int i,j;
double t;
for (i=0;i<n-1;i++) {
for (j=i;j<n;j++) {
if (e[j]<e[i]) {
t = e[j];
e[j]=e[i];
e[i]=t;
t = a[j];
a[j]=a[i];
a[i]=t;
}
}
}
}
/*
density of states
Appendix C of the paper
assume that et[] is orderd
input et[0:3], *e
output dos
*/
void ATM_Dos(double *et, double *e, double *dos)
{
double e21, e31, e32, e41, e42, e43;
double e1,e2,e4;
/* Parameter adjustments */
--et;
#if 0
printf("ATM: %lf %lf %lf %lf %lf\n",*e,et[1],et[2],et[3],et[4]);
#endif
e21 = et[2] - et[1];
e31 = et[3] - et[1];
e32 = et[3] - et[2];
e41 = et[4] - et[1];
e42 = et[4] - et[2];
e43 = et[4] - et[3];
if (*e < et[1]) {
*dos = 0.;
} else if (*e > et[1] && *e < et[2]) {
e1=(*e - et[1]);
*dos = 3.0 * e1*e1 / (e21 * e31 * e41);
} else if (*e > et[2] && *e < et[3]) {
e2=(*e - et[2]);
*dos = (e21 * 3. + e2 * 6. - (e31 + e42) * 3. * e2 * e2
/ (e32 * e42)) / (e31 * e41);
} else if (*e > et[3] && *e < et[4]) {
e4= (et[4] - *e);
*dos = 3.0* e4*e4 / (e41 * e42 * e43);
} else if (*e > et[4]) {
*dos = 0.;
}
#if 0
printf("ATM_Dos: %lf %lf %lf %lf %lf->%lf\n",*e, et[1],et[2],et[3],et[4],*dos);
#endif
}
/*
Appendix B of the paper
In the Appendix B, integrated weight is written, differenciate it.
assume that et[] is ordered.
input et[0:3], at[0:3],*e
output spectrum
<at> = sum_i at[i] w[i]
w[i] is a function of et[i]
An integrated w[i] is written in the paper.
*/
void ATM_Spectrum(double *et,double *at, double *e, double *spectrum)
{
double a21, a31, a32, a41;
double e21, e31, e32, e41, e42, e43;
double a42, a43;
double dos;
/* Parameter adjustments , --- f2c technique */
--at;
ATM_Dos(et, e, &dos);
--et;
#if 0
printf("DOS-> %lf %lf\n",*e,dos);
printf("%lf %lf %lf %lf\n",et[1],et[2],et[3],et[4]);
#endif
e21 = et[2] - et[1];
e31 = et[3] - et[1];
e32 = et[3] - et[2];
e41 = et[4] - et[1];
e42 = et[4] - et[2];
e43 = et[4] - et[3];
a21 = at[2] - at[1];
a31 = at[3] - at[1];
a32 = at[3] - at[2];
a41 = at[4] - at[1];
a42 = at[4] - at[2];
a43 = at[4] - at[3];
if (*e < et[1]) {
*spectrum = 0.;
} else if (*e > et[1] && *e < et[2]) {
*spectrum = dos * (at[1] + (*e - et[1]) * .33333333333333331 * (a21 /
e21 + a31 / e31 + a41 / e41));
} else if (*e > et[2] && *e < et[3]) {
*spectrum = dos * (at[1] + (a21 + e21 * a31 / e31 + e21 * a41 / e41) *
.33333333333333331 * (et[3] - *e) / e32 + (at[4] - at[1] - (
e43 * a41 / e41 + e43 * a42 / e42 + a43) * .33333333333333331)
* (*e - et[2]) / e32);
} else if (*e > et[3] && *e < et[4]) {
*spectrum = dos * (at[4] + (*e - et[4]) * .33333333333333331 * (a41 /
e41 + a42 / e42 + a43 / e43));
} else if (*e > et[4]) {
*spectrum = 0.;
}
}
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