Goldstone.hpp

#pragma once
#include "Coulomb/YkTable.hpp"
#include "HF/Breit.hpp"
#include "HF/HartreeFock.hpp"
#include "MBPT/SpinorMatrix.hpp"
#include "Maths/Grid.hpp"
#include "Wavefunction/DiracSpinor.hpp"
#include <memory>
#include <vector>
 
namespace MBPT {
 
//------------------------------------------------------------------------------
//! Class to construct Feynman diagrams, Green's functions and polarisation op.
class Goldstone {
 
  // Pointer to shared radial grid (full grid)
  std::shared_ptr<const Grid> m_grid;
 
  using Basis = std::vector<DiracSpinor>;
  std::pair<Basis, Basis> m_basis;
  Coulomb::YkTable m_Yeh;
 
  // Parameters of the sub-grid: initial/final points, stride
  std::size_t m_i0, m_stride, m_subgrid_points;
 
  int m_n_min_core;
  bool m_include_G;
 
  std::optional<HF::Breit> m_Br{};
 
public:
  Goldstone(const std::vector<DiracSpinor> &basis,
            const std::vector<DiracSpinor> &core, std::size_t i0,
            std::size_t stride, std::size_t size, int n_min_core = 1,
            bool include_G = false, const HF::Breit *Br = nullptr);
 
  //! Calculate Direct part of correlation potential
  GMatrix Sigma_direct(int kappa_v, double en_v,
                       const std::vector<double> &fk = {},
                       const std::vector<double> &etak = {},
                       int n_max_core = 99) const;
 
  //! Calculate Exchange part of correlation potential.
  //! @details fk are effective screening factors, applied to the multipole k
  //! of the outer Coulomb line; with fk_both_lines, also to the multipole of
  //! the inner line (inside P^k), i.e., f_k * f_l.
  GMatrix Sigma_exchange(int kappa_v, double en_v,
                         const std::vector<double> &fk = {},
                         bool fk_both_lines = false) const;
 
  // Calculate both parts of correlation potential.
  GMatrix Sigma_both(int kappa_v, double en_v,
                     const std::vector<double> &fk = {},
                     const std::vector<double> &etak = {}, int n_max_core = 99,
                     bool fk_both_lines = false) const;
 
  // Calculates 2-body Breit correction to correlation potential. Must have Breit
  GMatrix dSigma_Breit2(int kappa_v, double en_v,
                        const std::vector<double> &fk = {},
                        const std::vector<double> &etak = {},
                        int n_max_core = 99, int m_max_n_breit = -1) const;
 
  const std::pair<Basis, Basis> &basis() const { return m_basis; }
  const Coulomb::YkTable &Yeh() const { return m_Yeh; }
 
  std::size_t stride() const { return m_stride; }
  int n_min() const { return m_n_min_core; }
  int lmax() const { return DiracSpinor::max_l(m_basis.second); }
 
private:
  inline double get_k(int k, const std::vector<double> &f) const {
    const auto sk = std::size_t(k);
    return sk < f.size() ? f[sk] : 1.0;
  }
};
 
} // namespace MBPT