Update fix_eco_force.h

namespace LAMMPS_NS {

#define FIX_ECO_FORCE_MAX_NEIGHBORS 24

class FixECOForce : public Fix {

  public:

    struct Nbr {

      int n;                    // # of neighbors

      tagint id[24];            // IDs of each neighbor

      tagint id[FIX_ECO_FORCE_MAX_NEIGHBORS];       // IDs of each neighbor

                                // if center atom is owned, these are local IDs

                                // if center atom is ghost, these are global IDs

      double duchi;             // potential derivative

      double delta[24][3];      // difference vectors

      double delta[FIX_ECO_FORCE_MAX_NEIGHBORS][3]; // difference vectors

      double real_phi[2][3];    // real part of wave function

      double imag_phi[2][3];    // imaginary part of wave function

    };