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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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pp2 Normal file
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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);
double u[n + 1];
srand(time(NULL));
for (int i = 0; i < n + 1; ++i) {
u[i] = (double) rand() / RAND_MAX;
}
@ -44,18 +42,18 @@ void random_gauss(double *z, const int n) {
// 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]);
z[i] = z[i] * cos(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[i] = z[i] * cos(two_pi * u[i + 1]);
}
z[n] = sqrt(-2.0 * log(u[n]));
z[n] = z[n] * cos(two_pi * u[n + 1]);
z[n - 1] = sqrt(-2.0 * log(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;
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;
double rnd[3], fact_a, fact_b, sq_dt, q, u;
sq_dt = sqrt(dt);
// 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];
for (int j = 0; j < 3; ++j) {
d2_old += d_old[j] * d_old[j];
}
psi_old = psi(a, r_old, 3);
*energy = 0.0;
*accept = 0.0;
n_accept = 0;
@ -24,39 +28,41 @@ void variational_montecarlo(double a, const int nmax, double dt,
// Compute and accumulate the local energy
*energy += e_loc(a, r_old, 3);
// Compute new position
// Compute new position (correct variance of sampled Gaussian)
random_gauss(rnd, 3);
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
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];
for (int j = 0; j < 3; ++j) {
d2_new += d_new[j] * d_new[j];
}
psi_new = psi(a, r_new, 3);
// 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]);
for (int j = 0; j < 3; ++j) {
fact_b += (d_new[j] + d_old[j]) * (r_new[j] - r_old[j]);
}
fact_exp = exp(fact_b - fact_a);
aval = fact_exp * psi_new / psi_old;
fact_a = 0.5 * dt * (d2_new - d2_old) + fact_b;
q = psi_new / psi_old;
q = exp(-fact_a) * q * q;
u = (double) rand() / RAND_MAX;
if (u <= aval) {
if (u <= q) {
n_accept += 1;
for (int j = 0; j < 3; ++j) {
r_old[j] = r_new[j];
d_old[j] = d_new[j];
}
d2_old = d2_new;
psi_old = psi_new;
n_accept += 1;
}
}
*energy /= nmax;