GMullikenDomain.hpp

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// This file is part of GQCG-GQCP.
//
// Copyright (C) 2017-2020  the GQCG developers
//
// GQCG-GQCP is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// GQCG-GQCP is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with GQCG-GQCP.  If not, see <http://www.gnu.org/licenses/>.
 
#pragma once
 
 
#include "Basis/Transformations/GTransformation.hpp"
#include "Domain/DiscreteDomain.hpp"
#include "Mathematical/Representation/SquareMatrix.hpp"
 
 
namespace GQCP {
 
 
template <typename _Scalar>
class GMullikenDomain:
    public DiscreteDomain {
public:
    using DiscreteDomain::DiscreteDomain;
 
    // The expansion scalar type used for a Mulliken domain: real or complex.
    using Scalar = _Scalar;
 
    SquareMatrix<Scalar> partitionMatrix(const GTransformation<Scalar>& C) const {
 
        const auto M = C.numberOfOrbitals();
        const auto K = M / 2;
 
        // Set up the top-left (alpha) and bottom-right (beta) blocks of the total partition matrix.
        SquareMatrix<Scalar> P = SquareMatrix<Scalar>::Zero(M);
 
        auto P_component = SquareMatrix<Scalar>::PartitionMatrix(this->domain_indices, K);
        P.topLeftCorner(K, K) = P_component;
        P.bottomRightCorner(K, K) = P_component;
 
        return P;
    }
 
 
    GTransformation<Scalar> projectionMatrix(const GTransformation<Scalar>& C) const { return GTransformation<Scalar> {C.inverse().matrix() * this->partitionMatrix(C) * C.matrix()}; }
};
 
 
}  // namespace GQCP