effective_potential_non_local.hpp

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#pragma once
 
/**
 * EffectiveNonlocalPotential — abstract interface for the effective
 * D-matrix computation (QE's "newd").
 *
 * Combines the bare D_ij^ion matrix with the G-space integral of
 * V_eff(G) × Q_ij(G) × e^{-iG·τ} to produce the effective D-matrix
 * used in the non-local Hamiltonian.
 *
 * Implements Eq. (13) of K. Laasonen, A. Pasquarello, R. Car, C. Lee &
 * D. Vanderbilt, Phys. Rev. B 47, 10142 (1993), with V_eff their Eq. (12).
 * For a PAW dataset the same integral is D̂_ij, Eq. (44) of G. Kresse &
 * D. Joubert, Phys. Rev. B 59, 1758 (1999).
 */
 
#include <complex>
#include <vector>
 
#include "layer_0_core/types/init.hpp"
 
namespace q3 {
 
// Forward declarations
class Crystal;
class PlanewaveBasis;
 
class EffectiveNonlocalPotential {
  public:
    virtual ~EffectiveNonlocalPotential() = default;
 
    /**
     * Compute the effective D-matrix for all atoms.
     *
     * @param crystal_structure    Crystal structure with atom positions.
     * @param planewave_basis     Plane-wave basis set.
     * @param total_potential_g    Total effective potential V_eff(G).
     * @return effective_d_matrix[atom_index][projector_i * nproj + projector_j]
     */
    [[nodiscard]] virtual std::vector<std::vector<Real>>
    compute(const Crystal& crystal_structure,
            const PlanewaveBasis& planewave_basis,
            const std::vector<Complex>& total_potential_g) const = 0;
};
 
} // namespace q3