mirror of https://github.com/TREX-CoE/qmc-lttc.git
94 lines
2.2 KiB
C
94 lines
2.2 KiB
C
#include "hydrogen.h"
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#include "qmc_stats.h"
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void variational_montecarlo(double a, const int nmax, double dt,
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double *energy, double *accept) {
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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], 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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drift(a, r_old, d_old, 3);
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d2_old = 0.0;
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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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for (int i = 0; i < nmax; ++i) {
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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 (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] * sq_dt;
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}
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// New WF and acceptance probability
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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 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_b = 0.0;
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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_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 <= 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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}
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}
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*energy /= nmax;
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*accept = (double) n_accept / nmax;
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}
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int main() {
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const double a = 1.2;
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const double dt = 1.0;
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const long nmax = 1e5;
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int nruns = 30;
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srand(time(NULL));
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double ene[nruns], acc[nruns], obs[2];
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for (int i = 0; i < nruns; ++i) {
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variational_montecarlo(a, nmax, dt, &ene[i], &acc[i]);
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}
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ave_error(ene, nruns, obs);
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printf("E = %.5lf +/- %.5lf\n", obs[0], obs[1]);
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ave_error(acc, nruns, obs);
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printf("A = %.5lf +/- %.5lf\n", obs[0], obs[1]);
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return 0;
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}
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