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https://github.com/TREX-CoE/qmc-lttc.git
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Fixed VMC
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0bbfb469c9
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c55a1bb1f1
10
qmc_stats.h
10
qmc_stats.h
@ -33,8 +33,6 @@ void random_gauss(double *z, const int n) {
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const double two_pi = 2.0 * acos(-1.0);
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double u[n + 1];
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srand(time(NULL));
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for (int i = 0; i < n + 1; ++i) {
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u[i] = (double) rand() / RAND_MAX;
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}
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@ -44,18 +42,18 @@ void random_gauss(double *z, const int n) {
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// n is even
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for (int i = 0; i < n; i+=2) {
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z[i] = sqrt(-2.0 * log(u[i]));
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z[i] = z[i] * cos(two_pi * u[i + 1]);
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z[i + 1] = z[i] * sin(two_pi * u[i + 1]);
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z[i] = z[i] * cos(two_pi * u[i + 1]);
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}
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}
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else {
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// n is odd
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for (int i = 0; i < n - 1; i+=2) {
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z[i] = sqrt(-2.0 * log(u[i]));
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z[i] = z[i] * cos(two_pi * u[i + 1]);
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z[i + 1] = z[i] * sin(two_pi * u[i + 1]);
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z[i] = z[i] * cos(two_pi * u[i + 1]);
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}
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z[n] = sqrt(-2.0 * log(u[n]));
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z[n] = z[n] * cos(two_pi * u[n + 1]);
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z[n - 1] = sqrt(-2.0 * log(u[n - 1]));
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z[n - 1] = z[n - 1] * cos(two_pi * u[n]);
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}
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}
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@ -6,17 +6,21 @@ void variational_montecarlo(double a, const int nmax, double dt,
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int n_accept;
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double r_old[3], r_new[3], psi_old, psi_new;
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double d_old[3], d_new[3], d2_old, d2_new;
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double rnd[3], aval, fact_a, fact_b, fact_exp, u;
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double rnd[3], fact_a, fact_b, sq_dt, q, u;
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sq_dt = sqrt(dt);
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// Initial position
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random_gauss(r_old, 3);
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psi_old = psi(a, r_old, 3) * psi(a, r_old, 3);
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drift(a, r_old, d_old, 3);
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d2_old = 0.0;
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for (int i = 0; i < 3; ++i) {
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d2_old += d_old[i] * d_old[i];
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for (int j = 0; j < 3; ++j) {
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d2_old += d_old[j] * d_old[j];
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}
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psi_old = psi(a, r_old, 3);
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*energy = 0.0;
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*accept = 0.0;
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n_accept = 0;
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@ -24,39 +28,41 @@ void variational_montecarlo(double a, const int nmax, double dt,
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// Compute and accumulate the local energy
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*energy += e_loc(a, r_old, 3);
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// Compute new position
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// Compute new position (correct variance of sampled Gaussian)
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random_gauss(rnd, 3);
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for (int j = 0; j < 3; ++j) {
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r_new[j] = r_old[j] + dt * d_old[j] + rnd[j];
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r_new[j] = r_old[j] + dt * d_old[j] + rnd[j] * sq_dt;
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}
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// New WF and acceptance probability
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psi_new = psi(a, r_new, 3) * psi(a, r_new, 3);
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drift(a, r_new, d_new, 3);
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d2_new = 0.0;
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for (int i = 0; i < 3; ++i) {
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d2_new += d_new[i] * d_new[i];
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for (int j = 0; j < 3; ++j) {
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d2_new += d_new[j] * d_new[j];
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}
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psi_new = psi(a, r_new, 3);
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// Compute the ratio of probabilities q
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fact_a = 0.5 * dt * (d2_new - d2_old);
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fact_b = 0.0;
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for (int i = 0; i < 3; ++i) {
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fact_b += (d_new[i] + d_old[i]) * (r_new[i] - r_old[i]);
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for (int j = 0; j < 3; ++j) {
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fact_b += (d_new[j] + d_old[j]) * (r_new[j] - r_old[j]);
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}
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fact_exp = exp(fact_b - fact_a);
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aval = fact_exp * psi_new / psi_old;
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fact_a = 0.5 * dt * (d2_new - d2_old) + fact_b;
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q = psi_new / psi_old;
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q = exp(-fact_a) * q * q;
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u = (double) rand() / RAND_MAX;
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if (u <= aval) {
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if (u <= q) {
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n_accept += 1;
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for (int j = 0; j < 3; ++j) {
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r_old[j] = r_new[j];
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d_old[j] = d_new[j];
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}
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d2_old = d2_new;
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psi_old = psi_new;
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n_accept += 1;
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}
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}
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*energy /= nmax;
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