CALCT2 Function

FUNCTION CALCT2(NI, NEL, G1, ALAT, CST)
    use constants, only: dp
    use SystemData, only: BasisFN, kvec, k_lattice_constant, TUEG2
    IMPLICIT NONE
    INTEGER NEL, NI(NEL), I, J
    TYPE(BasisFN) G1(*)
    real(dp) ALAT(4), CST, TMAT, CALCT2

    CALCT2 = 0.0_dp

    !===============================
    if(TUEG2) then
        DO J = 1, NEL
            I = NI(J)
            TMAT = real(kvec(I, 1)**2 + kvec(I, 2)**2 + kvec(I, 3)**2, dp)
            TMAT = 0.5_dp * TMAT * k_lattice_constant**2
            CALCT2 = CALCT2 + TMAT
        end do
        return
    end if ! TUEG2
    !===============================
    DO J = 1, NEL
        I = NI(J)
        TMAT = ((ALAT(1)**2) * ((G1(I)%K(1)**2) / (ALAT(1)**2) + &
                                (G1(I)%K(2)**2) / (ALAT(2)**2) + &
                                (G1(I)%K(3)**2) / (ALAT(3)**2)))
        TMAT = TMAT * CST
        CALCT2 = CALCT2 + TMAT
    end do
    RETURN
END FUNCTION CALCT2