SpinlessFermionSite.h

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#ifndef SPINLESSFERMIONSITE_H_
#define SPINLESSFERMIONSITE_H_
 
#include "symmetry/kind_dummies.h"
#include "symmetry/U0.h"
#include "symmetry/U1.h"
 
template <typename Symmetry_>
class SpinlessFermionSite
{
    typedef double Scalar;
    typedef Symmetry_ Symmetry;
    typedef SiteOperatorQ<Symmetry,Eigen::Matrix<Scalar,Eigen::Dynamic,Eigen::Dynamic> > OperatorType;
    
public:
    
    SpinlessFermionSite();
    
    OperatorType Id_1s() const {return Id_1s_;}
    OperatorType F_1s() const {return F_1s_;}
    
    OperatorType c_1s() const { return c_1s_;}
    OperatorType cdag_1s() const { return cdag_1s_;}
    OperatorType n_1s() const {return n_1s_;}
    OperatorType nph_1s() const {return nph_1s_;}
    
    Qbasis<Symmetry> basis_1s() const {return basis_1s_;}
    
protected:
    
    void fill_basis();
    void fill_SiteOps();
    
    typename Symmetry_::qType getQ (int Delta) const;
    
    Qbasis<Symmetry> basis_1s_;
    
    OperatorType Id_1s_; //identity
    OperatorType F_1s_; //Fermionic sign
    
    OperatorType c_1s_; //annihilation
    OperatorType cdag_1s_; //creation
    OperatorType n_1s_; //particle number
    OperatorType nph_1s_; //particle number-1/2 (particle-hole symmetric)
};
 
template<typename Symmetry_>
SpinlessFermionSite<Symmetry_>::
SpinlessFermionSite()
{
    fill_basis();
    fill_SiteOps();
}
 
template <typename Symmetry_>
void SpinlessFermionSite<Symmetry_>::
fill_SiteOps()
{
    // create operators for one site
    Id_1s_ = OperatorType(Symmetry::qvacuum(),basis_1s_);
    F_1s_  = OperatorType(Symmetry::qvacuum(),basis_1s_);
    
    c_1s_    = OperatorType(getQ(-1),basis_1s_);
    cdag_1s_ = OperatorType(getQ(+1),basis_1s_);
    n_1s_    = OperatorType(Symmetry::qvacuum(),basis_1s_);
    nph_1s_  = OperatorType(Symmetry::qvacuum(),basis_1s_);
    
    Id_1s_("empty","empty") = 1.;
    Id_1s_("occup","occup") = 1.;
    
    F_1s_("empty","empty") = 1.;
    F_1s_("occup","occup") = -1.;
    
    c_1s_("empty","occup")  = 1.;
    cdag_1s_("occup","empty")  = 1.;
    
//  cout << "c_1s_=" << MatrixXd(c_1s_.template plain<double>().data) << endl;
//  cout << "cdag_1s_=" << MatrixXd(cdag_1s_.template plain<double>().data) << endl;
    
    n_1s_("occup","occup") = 1.;
    
    nph_1s_("occup","occup") = +0.5;
    nph_1s_("empty","empty") = -0.5;
    
    return;
}
 
template<typename Symmetry_>
void SpinlessFermionSite<Symmetry_>::
fill_basis()
{
    if constexpr (std::is_same<Symmetry, Sym::U0>::value) //U0
    {
        typename Symmetry::qType Q = {};
        Eigen::Index inner_dim;
        std::vector<std::string> ident;
        
        ident.push_back("empty");
        ident.push_back("occup");
        inner_dim = 2;
        basis_1s_.push_back(Q,inner_dim,ident);
        ident.clear();
    }
    else if constexpr (std::is_same<Symmetry, Sym::U1<Sym::ChargeU1> >::value) //charge U1
    {
        typename Symmetry::qType Q;
        Eigen::Index inner_dim;
        std::vector<std::string> ident;
        
        Q = {0};
        ident.push_back("empty");
        inner_dim = 1;
        basis_1s_.push_back(Q,inner_dim,ident);
        ident.clear();
        
        Q = {1};
        inner_dim = 1;
        ident.push_back("occup");
        basis_1s_.push_back(Q,inner_dim,ident);
        ident.clear();
    }
}
 
template<typename Symmetry_>
typename Symmetry_::qType SpinlessFermionSite<Symmetry_>::
getQ (int Delta) const
{
    if constexpr (Symmetry::IS_TRIVIAL) {return {};}
    else if constexpr (Symmetry::Nq == 1) 
    {
        if constexpr (Symmetry::kind()[0] == Sym::KIND::N) //return particle number as good quantum number.
        {
            typename Symmetry::qType out;
            out = {Delta};
            return out;
        }
        else if constexpr (Symmetry::kind()[0] == Sym::KIND::Z2) //return parity as good quantum number.
        {
            typename Symmetry::qType out;
            out = {posmod<2>(Delta)};
            return out;
        }
        else {assert(false and "Ill-defined KIND of the used Symmetry.");}
    }
    static_assert("You've inserted a symmetry which can not be handled by SpinlessFermionSite.");
}
 
#endif //FERMIONSITE_H_