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Fixed VMC

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This commit is contained in:
Panadestein 2021-04-27 20:06:31 +02:00
parent 0bbfb469c9
commit c55a1bb1f1
3 changed files with 3000029 additions and 23 deletions
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10
qmc_stats.h
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@ -33,8 +33,6 @@ void random_gauss(double *z, const int n) {
const double two_pi = 2.0 * acos(-1.0); const double two_pi = 2.0 * acos(-1.0);
double u[n + 1]; double u[n + 1];
srand(time(NULL));
for (int i = 0; i < n + 1; ++i) { for (int i = 0; i < n + 1; ++i) {
u[i] = (double) rand() / RAND_MAX; u[i] = (double) rand() / RAND_MAX;
} }
@ -44,18 +42,18 @@ void random_gauss(double *z, const int n) {
// n is even // n is even
for (int i = 0; i < n; i+=2) { for (int i = 0; i < n; i+=2) {
z[i] = sqrt(-2.0 * log(u[i])); 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[i + 1] = z[i] * sin(two_pi * u[i + 1]);
z[i] = z[i] * cos(two_pi * u[i + 1]);
} }
} }
else { else {
// n is odd // n is odd
for (int i = 0; i < n - 1; i+=2) { for (int i = 0; i < n - 1; i+=2) {
z[i] = sqrt(-2.0 * log(u[i])); 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[i + 1] = z[i] * sin(two_pi * u[i + 1]);
z[i] = z[i] * cos(two_pi * u[i + 1]);
} }
z[n] = sqrt(-2.0 * log(u[n])); z[n - 1] = sqrt(-2.0 * log(u[n - 1]));
z[n] = z[n] * cos(two_pi * u[n + 1]); z[n - 1] = z[n - 1] * cos(two_pi * u[n]);
} }
} }

40
vmc_metropolis.c
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@ -6,17 +6,21 @@ void variational_montecarlo(double a, const int nmax, double dt,
int n_accept; int n_accept;
double r_old[3], r_new[3], psi_old, psi_new; double r_old[3], r_new[3], psi_old, psi_new;
double d_old[3], d_new[3], d2_old, d2_new; double d_old[3], d_new[3], d2_old, d2_new;
double rnd[3], aval, fact_a, fact_b, fact_exp, u; double rnd[3], fact_a, fact_b, sq_dt, q, u;
sq_dt = sqrt(dt);
// Initial position // Initial position
random_gauss(r_old, 3); random_gauss(r_old, 3);
psi_old = psi(a, r_old, 3) * psi(a, r_old, 3);
drift(a, r_old, d_old, 3); drift(a, r_old, d_old, 3);
d2_old = 0.0; d2_old = 0.0;
for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) {
d2_old += d_old[i] * d_old[i]; d2_old += d_old[j] * d_old[j];
} }
psi_old = psi(a, r_old, 3);
*energy = 0.0; *energy = 0.0;
*accept = 0.0; *accept = 0.0;
n_accept = 0; n_accept = 0;
@ -24,39 +28,41 @@ void variational_montecarlo(double a, const int nmax, double dt,
// Compute and accumulate the local energy // Compute and accumulate the local energy
*energy += e_loc(a, r_old, 3); *energy += e_loc(a, r_old, 3);
// Compute new position // Compute new position (correct variance of sampled Gaussian)
random_gauss(rnd, 3); random_gauss(rnd, 3);
for (int j = 0; j < 3; ++j) { for (int j = 0; j < 3; ++j) {
r_new[j] = r_old[j] + dt * d_old[j] + rnd[j]; r_new[j] = r_old[j] + dt * d_old[j] + rnd[j] * sq_dt;
} }
// New WF and acceptance probability // New WF and acceptance probability
psi_new = psi(a, r_new, 3) * psi(a, r_new, 3);
drift(a, r_new, d_new, 3); drift(a, r_new, d_new, 3);
d2_new = 0.0; d2_new = 0.0;
for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) {
d2_new += d_new[i] * d_new[i]; d2_new += d_new[j] * d_new[j];
} }
psi_new = psi(a, r_new, 3);
// Compute the ratio of probabilities q // Compute the ratio of probabilities q
fact_a = 0.5 * dt * (d2_new - d2_old);
fact_b = 0.0; fact_b = 0.0;
for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) {
fact_b += (d_new[i] + d_old[i]) * (r_new[i] - r_old[i]); fact_b += (d_new[j] + d_old[j]) * (r_new[j] - r_old[j]);
} }
fact_exp = exp(fact_b - fact_a); fact_a = 0.5 * dt * (d2_new - d2_old) + fact_b;
aval = fact_exp * psi_new / psi_old;
q = psi_new / psi_old;
q = exp(-fact_a) * q * q;
u = (double) rand() / RAND_MAX; u = (double) rand() / RAND_MAX;
if (u <= aval) { if (u <= q) {
n_accept += 1;
for (int j = 0; j < 3; ++j) { for (int j = 0; j < 3; ++j) {
r_old[j] = r_new[j]; r_old[j] = r_new[j];
d_old[j] = d_new[j]; d_old[j] = d_new[j];
} }
d2_old = d2_new;
psi_old = psi_new; psi_old = psi_new;
n_accept += 1;
} }
} }
*energy /= nmax; *energy /= nmax;