Calculations/Dipolar-Gas-Simulator/+Variational2D/@Calculator/calculateVDkWithCutoff.m

function VDk = calculateVDkWithCutoff(~, rcut, Transf, Params, VParams)
% == Calculating the DDI potential in Fourier space with appropriate cutoff == %

    % Interaction in K space
    QX              = Transf.KX*VParams.ell_eff/sqrt(2);
    QY              = Transf.KY*VParams.ell_eff/sqrt(2);

    Qsq             = QX.^2 + QY.^2;
    absQ            = sqrt(Qsq);
    QDsq            = QX.^2*cos(Params.phi)^2 + QY.^2*sin(Params.phi)^2;
    
    % Bare interaction
    Fpar            = -1 + 3*sqrt(pi)*QDsq.*erfcx(absQ)./absQ;
    Fperp           = 2 - 3*sqrt(pi).*absQ.*erfcx(absQ);
    Fpar(absQ == 0) = -1; 
    % Fpar(isinf(Fpar)) = -1;
    
    % Full DDI
    VDk             = (Fpar*sin(Params.theta)^2 + Fperp*cos(Params.theta)^2);
    
    % Implementing a cutoff:
    VDr             = ifftn(VDk);
    VDr             = fftshift(VDr);
    
    R               = sqrt(Transf.X.^2+Transf.Y.^2) < 0.9*rcut;
    VDr             = VDr.*double(R);
    VDr             = ifftshift(VDr);
    VDk             = fftn(VDr);

end