main.cpp

#include "gfnff_interface_c.h"
#include <iostream>

void run_singlepoint_test() {
  const int nat = 24;
  int at[nat] = {6, 7, 6, 7, 6, 6, 6, 8, 7, 6, 8, 7,
                 6, 6, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
  double xyz[nat][3] = {
      {2.02799738646442, 0.09231312124713, -0.14310895950963},
      {4.75011007621000, 0.02373496014051, -0.14324124033844},
      {6.33434307654413, 2.07098865582721, -0.14235306905930},
      {8.72860718071825, 1.38002919517619, -0.14265542523943},
      {8.65318821103610, -1.19324866489847, -0.14231527453678},
      {6.23857175648671, -2.08353643730276, -0.14218299370797},
      {5.63266886875962, -4.69950321056008, -0.13940509630299},
      {3.44931709749015, -5.48092386085491, -0.14318454855466},
      {7.77508917214346, -6.24427872938674, -0.13107140408805},
      {10.30229550927022, -5.39739796609292, -0.13672168520430},
      {12.07410272485492, -6.91573621641911, -0.13666499342053},
      {10.70038521493902, -2.79078533715849, -0.14148379504141},
      {13.24597858727017, -1.76969072232377, -0.14218299370797},
      {7.40891694074004, -8.95905928176407, -0.11636933482904},
      {1.38702118184179, 2.05575746325296, -0.14178615122154},
      {1.34622199478497, -0.86356704498496, 1.55590600570783},
      {1.34624089204623, -0.86133716815647, -1.84340893849267},
      {5.65596919189118, 4.00172183859480, -0.14131371969009},
      {14.67430918222276, -3.26230980007732, -0.14344911021228},
      {13.50897177220290, -0.60815166181684, 1.54898960808727},
      {13.50780014200488, -0.60614855212345, -1.83214617078268},
      {5.41408424778406, -9.49239668625902, -0.11022772492007},
      {8.31919801555568, -9.74947502841788, 1.56539243085954},
      {8.31511620712388, -9.76854236502758, -1.79108242206824}};

  double energy;
  double gradient[nat][3];
  double sigma[3][3];  // stress tensor (zero for non-PBC)
  int iostat;
  const char *solvent = "h2o";

  // Initialize the Fortran calculator
  c_gfnff_calculator calc = c_gfnff_calculator_init(
      nat, // int nat
      at,  // int *at
           // &xyz[0][0],  // double xyz[3][24]
      xyz,
      0,      // molecular charge
      1,      // printlevel directive (0 is off)
      solvent // solvent string
           // No iostat in this call
  );

  if (calc.ptr == NULL) {
    std::cerr << "Error initializing gfnff calculator.\n";
    return;
  }

  // Run the singlepoint calculation (nullptr lattice: non-PBC, reuse stored)
  c_gfnff_calculator_singlepoint(&calc, nat, at, xyz, &energy, gradient,
                                 sigma, nullptr, &iostat);

  if (iostat == 0) {
    std::cout << "Singlepoint calculation successful.\n";
    std::cout << "Energy: " << energy << "\n";

    // Print the gradient
    for (int i = 0; i < 3; ++i) {
      for (int j = 0; j < 1; ++j) {
        std::cout << "Gradient[" << j << "][" << i << "] = " << gradient[j][i]
                  << "\n";
      }
    }

    // Print the stress tensor (molecular — expect zeros from C interface)
    std::cout << "Sigma (molecular, should be zeroed):\n";
    for (int i = 0; i < 3; ++i)
      for (int j = 0; j < 3; ++j)
        std::cout << "  sigma[" << i << "][" << j << "] = " << sigma[i][j] << "\n";
  } else {
    std::cerr << "Singlepoint calculation failed with iostat = " << iostat
              << "\n";
  }

  // Print results to stdout
  int iunit = 6;
  c_gfnff_calculator_results(&calc, iunit);

  // Deallocate the Fortran calculator
  c_gfnff_calculator_deallocate(&calc);
}

void run_pbc_singlepoint_test() {
  // SiO2 alpha-quartz unit cell (9 atoms, hexagonal lattice)
  const int nat = 9;
  int at[nat] = {8, 8, 8, 8, 8, 8, 14, 14, 14};
  double xyz[nat][3] = {
      { 2.82781861325240,  2.96439280874170,  3.12827803849279},
      { 7.19124230791576,  0.98723342603994,  4.89004701836746},
      { 4.95491880597601,  4.82830910314898,  8.74847811174740},
      { 0.19290883043307,  2.30645007856310,  8.72969832061507},
      {-2.01592208020090,  6.16478744235115,  4.87273962147340},
      { 0.66183062221384,  7.07392578563696,  0.27767968372345},
      { 4.55701736204879,  0.06291337111965,  3.31745840478609},
      {-2.10064209975148,  3.63969476409878,  6.81014625000326},
      { 2.31009832827224,  4.12572862149043,  0.08842485276656}};
  // Each C row maps to a Fortran column (lattice vector)
  const double a = 9.28422449595511046;
  const double c = 10.21434769907115;
  double lattice[3][3] = {
      {a,        0.0,                    0.0},  // a1
      {a * -0.5, a * 0.86602540378443865, 0.0},  // a2
      {0.0,      0.0,                    c  }};  // a3
  int npbc = 3;

  double energy;
  double gradient[nat][3];
  double sigma[3][3];  // stress tensor
  int iostat;

  c_gfnff_calculator calc = c_gfnff_calculator_init_pbc(
      nat, at, xyz, 0, 1, lattice, npbc);

  if (calc.ptr == NULL) {
    std::cerr << "Error initializing PBC gfnff calculator.\n";
    return;
  }

  c_gfnff_calculator_singlepoint(&calc, nat, at, xyz, &energy, gradient,
                                 sigma, lattice, &iostat);

  if (iostat == 0) {
    std::cout << "PBC singlepoint calculation successful.\n";
    std::cout << "PBC Energy: " << energy << "\n";
    for (int i = 0; i < 3; ++i) {
      std::cout << "PBC Gradient[0][" << i << "] = " << gradient[0][i] << "\n";
    }

    // Print the PBC stress tensor
    std::cout << "Sigma (PBC):\n";
    for (int i = 0; i < 3; ++i)
      for (int j = 0; j < 3; ++j)
        std::cout << "  sigma[" << i << "][" << j << "] = " << sigma[i][j] << "\n";
  } else {
    std::cerr << "PBC singlepoint calculation failed with iostat = " << iostat
              << "\n";
  }

  int iunit = 6;
  c_gfnff_calculator_results(&calc, iunit);

  c_gfnff_calculator_deallocate(&calc);
}

int main() {
  run_singlepoint_test();
  run_pbc_singlepoint_test();
  return 0;
}