  A simple approximation within the framework of the hybrid methods for the
calculation of the electronic structure of solids is presented. By considering
only the diagonal elements of the perturbation operator (Hartree-Fock exchange
minus semilocal exchange) calculated in the basis of the semilocal orbitals,
the computational time is drastically reduced, while keeping the accuracy of
the results obtained with hybrid functionals when applied without any
approximations.
