Multiplying the eigenvector equation for ϕα on the right by ψβj and summing over j, and multiplying the eigenvector equation for ψβ on the left by \(\phi^\alp...Multiplying the eigenvector equation for ϕα on the right by ψβj and summing over j, and multiplying the eigenvector equation for ψβ on the left by ϕαi and summing over i, and subtracting the two results yields