Latest developments and applications of double-hybrid density functionals

The neglect of non-local electron correlation effects is a serious drawback of common DFT methods. To remedy this, we have recently developed double-hybrid density functionals (X2PLYP family) [1,2], which add a second order perturbation correction for correlation to a standard hybrid functional in an empirical way. Here we give an overview of the extensions of our previous work. We discuss the analytical gradient for structure optimisations [3], the combination with an empirical dispersion correction (DFT-D) [4], and the computation of excitation energies in a time-dependent framework [5]. We present results for several benchmark sets and for some challenging applications. In all cases very accurate results are obtained at a reasonable computational expense. These show, that our method outperforms common (TD)DFT approaches and is even competitive to more sophisticated approaches like CCSD(T).