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mirror of https://github.com/TREX-CoE/qmc-lttc.git synced 2024-07-16 08:00:45 +02:00

Solutions in C up to 4

This commit is contained in:
Panadestein 2021-04-26 21:50:11 +02:00
parent 6eb6eed6db
commit f4d390972d
7 changed files with 154 additions and 0 deletions

1
.gitignore vendored
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@ -5,3 +5,4 @@ get_energ
get_var
qmc_uni
qmc_met
vmc

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@ -46,3 +46,17 @@ double kinetic(double a, double *r, const int l) {
double e_loc(double a, double *r, const int l) {
return kinetic(a, r, l) + potential(r, l);
}
void drift(double a, double *r, double *d, const int l) {
double rnorm, fact;
for (int i = 0; i < l; ++i) {
rnorm += r[i]*r[i];
}
rnorm = sqrt(rnorm);
fact = -a / rnorm;
for (int i = 0; i < l; ++i) {
d[i] = r[i] * fact;
}
}

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pp Executable file

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7
qmc_gaussian.c Normal file
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@ -0,0 +1,7 @@
#include <math.h>
#include <stdio.h>
double gaussian(double *r) {
// Pending
return 0;
}

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@ -1,5 +1,7 @@
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void ave_error(double *x, const int n, double obs[2]) {
// obs[1] --> mean and obs[2] --> err
@ -25,3 +27,35 @@ void ave_error(double *x, const int n, double obs[2]) {
}
}
void random_gauss(double *z, const int n) {
// Box Muller method
const double two_pi = 2.0 * acos(-1.0);
double u[n + 1];
srand(time(NULL));
for (int i = 0; i < n + 1; ++i) {
u[i] = (double) rand() / RAND_MAX;
}
if (!(n & 1)) {
// n is even
for (int i = 0; i < n; i+=2) {
z[i] = sqrt(-2.0 * log(u[i]));
z[i] = z[i] * cos(two_pi * u[i + 1]);
z[i + 1] = z[i] * sin(two_pi * u[i + 1]);
}
}
else {
// n is odd
for (int i = 0; i < n - 1; i+=2) {
z[i] = sqrt(-2.0 * log(u[i]));
z[i] = z[i] * cos(two_pi * u[i + 1]);
z[i + 1] = z[i] * sin(two_pi * u[i + 1]);
}
z[n] = sqrt(-2.0 * log(u[n]));
z[n] = z[n] * cos(two_pi * u[n + 1]);
}
}

11
tt.c Normal file
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@ -0,0 +1,11 @@
#include "qmc_stats.h"
int main() {
double rnd[3];
random_gauss(rnd, 3);
for (int i = 0; i < 3; ++i) {
printf("val %lf\n", rnd[i]);
}
return 0;
}

87
vmc_metropolis.c Normal file
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@ -0,0 +1,87 @@
#include "hydrogen.h"
#include "qmc_stats.h"
void variational_montecarlo(double a, const int nmax, double dt,
double *energy, double *accept) {
int n_accept;
double r_old[3], r_new[3], psi_old, psi_new;
double d_old[3], d_new[3], d2_old, d2_new;
double rnd[3], aval, fact_a, fact_b, fact_exp, u;
// Initial position
random_gauss(r_old, 3);
psi_old = psi(a, r_old, 3) * psi(a, r_old, 3);
drift(a, r_old, d_old, 3);
d2_old = 0.0;
for (int i = 0; i < 3; ++i) {
d2_old += d_old[i] * d_old[i];
}
*energy = 0.0;
*accept = 0.0;
n_accept = 0;
for (int i = 0; i < nmax; ++i) {
// Compute and accumulate the local energy
*energy += e_loc(a, r_old, 3);
// Compute new position
random_gauss(rnd, 3);
for (int j = 0; j < 3; ++j) {
r_new[j] = r_old[j] + dt * d_old[j] + rnd[j];
}
// New WF and acceptance probability
psi_new = psi(a, r_new, 3) * psi(a, r_new, 3);
drift(a, r_new, d_new, 3);
d2_new = 0.0;
for (int i = 0; i < 3; ++i) {
d2_new += d_new[i] * d_new[i];
}
// Compute the ratio of probabilities q
fact_a = 0.5 * dt * (d2_new - d2_old);
fact_b = 0.0;
for (int i = 0; i < 3; ++i) {
fact_b += (d_new[i] + d_old[i]) * (r_new[i] - r_old[i]);
}
fact_exp = exp(fact_b - fact_a);
aval = fact_exp * psi_new / psi_old;
u = (double) rand() / RAND_MAX;
if (u <= aval) {
for (int j = 0; j < 3; ++j) {
r_old[j] = r_new[j];
d_old[j] = d_new[j];
}
psi_old = psi_new;
n_accept += 1;
}
}
*energy /= nmax;
*accept = (double) n_accept / nmax;
}
int main() {
const double a = 1.2;
const double dt = 1.0;
const long nmax = 1e5;
int nruns = 30;
srand(time(NULL));
double ene[nruns], acc[nruns], obs[2];
for (int i = 0; i < nruns; ++i) {
variational_montecarlo(a, nmax, dt, &ene[i], &acc[i]);
}
ave_error(ene, nruns, obs);
printf("E = %.5lf +/- %.5lf\n", obs[0], obs[1]);
ave_error(acc, nruns, obs);
printf("A = %.5lf +/- %.5lf\n", obs[0], obs[1]);
return 0;
}