LindhardSusceptibility.h

/* Copyright 2017 Kristofer Björnson
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


#ifndef COM_DAFER45_TBTK_SOLVER_LINDHARD_SUSCEPTIBILITY
#define COM_DAFER45_TBTK_SOLVER_LINDHARD_SUSCEPTIBILITY

#include "TBTK/RPA/MomentumSpaceContext.h"
#include "TBTK/Solver/Susceptibility.h"

#include <complex>

namespace TBTK{
namespace Solver{

class LindhardSusceptibility : public Susceptibility{
public:
    LindhardSusceptibility(
        const RPA::MomentumSpaceContext &momentumSpaceContext
    );

    virtual ~LindhardSusceptibility();

    virtual LindhardSusceptibility* createSlave();

    virtual std::vector<std::complex<double>> calculateSusceptibility(
        const Index &index,
        const std::vector<std::complex<double>> &energies
    );
private:
    double *fermiDiracLookupTable;

    LindhardSusceptibility(
        const RPA::MomentumSpaceContext &momentumSpaceContext,
        int *kPlusQLookupTable,
        double *fermiDiracLookupTable
    );

    template<bool useKPlusQLookupTable/*, bool isSafeFromPoles*/>
    std::vector<std::complex<double>> calculateSusceptibilityLindhard(
        const Index &index,
        const std::vector<std::complex<double>> &energies
    );

    std::complex<double> getPoleTimesTwoFermi(
        std::complex<double> energy,
        double e2,
        double e1,
        double chemicalPotential,
        double temperature,
        int kPlusQLinearIndex,
        unsigned int meshPoint,
        unsigned int state2,
        unsigned int state1,
        unsigned int numOrbitals
    ) const;

    void generateKPlusQLookupTable();

    int* getKPlusQLookupTable();

    const int* getKPlusQLookupTable() const;

    template<bool useKPlusQLookupTable>
    int getKPlusQLinearIndex(
        unsigned int meshIndex,
        const std::vector<double> &k,
        int kLinearIndex
    ) const;

    int *kPlusQLookupTable;

    bool isMaster;
};

inline int* LindhardSusceptibility::getKPlusQLookupTable(){
    return kPlusQLookupTable;
}

inline const int* LindhardSusceptibility::getKPlusQLookupTable() const{
    return kPlusQLookupTable;
}

template<>
inline int LindhardSusceptibility::getKPlusQLinearIndex<false>(
    unsigned int meshIndex,
    const std::vector<double> &k,
    int kLinearIndex
) const{
    const RPA::MomentumSpaceContext &momentumSpaceContext
        = getMomentumSpaceContext();

    const std::vector<std::vector<double>> &mesh
        = momentumSpaceContext.getMesh();

    Index kPlusQIndex
        = momentumSpaceContext.getBrillouinZone().getMinorCellIndex(
            {mesh[meshIndex][0] + k[0], mesh[meshIndex][1] + k[1]},
            momentumSpaceContext.getNumMeshPoints()
        );
    return momentumSpaceContext.getModel().getHoppingAmplitudeSet().getFirstIndexInBlock(
        kPlusQIndex
    );
}

template<>
inline int LindhardSusceptibility::getKPlusQLinearIndex<true>(
    unsigned int meshIndex,
    const std::vector<double> &k,
    int kLinearIndex
) const{
    const RPA::MomentumSpaceContext &momentumSpaceContext
        = getMomentumSpaceContext();

    return kPlusQLookupTable[
        meshIndex*momentumSpaceContext.getMesh().size()
        + kLinearIndex/momentumSpaceContext.getNumOrbitals()
    ];
}

};  //End of namespace Solver
};  //End of namespace TBTK

#endif