The value of range-separation parameter based on IP tuning procedure () exhibits a troublesome dependence on system size.927, 284, 940, 188, 691 An alternative method to select is the global density-dependent (GDD) tuning procedure,642 in which the optimal value
is related to the average of the distance between an electron in the outer regions of a molecule and the exchange hole in the region of localized valence orbitals. The quantity is an empirical parameter for a given LRC functional, which was determined for LRC-PBE () and LRC-PBEh () using the def2-TZVPP basis set.642 (A slightly different value, , was determined for Q-Chem’s implementation of LRC-PBE.529) Since LRC-PBE() provides a better description of polarizabilities in polyacetylene as compared to 343, it is anticipated that using in place of may afford more accurate molecular properties, especially in conjugated systems. GDD tuning of an RSH functional is involving by setting the $rem variable OMEGA_GDD = TRUE. The electron density is obviously needed to compute in Eq. (5.18) and this is accomplished using the converged SCF density computed using the RSH functional with the value of given by the $rem variable OMEGA. The value of therefore depends, in principle, upon the value of OMEGA, although in practice it is not very sensitive to this value.
$comment The initial omega value has to set. $end $molecule 0 1 O -0.042500 0.091700 0.110000 H 0.749000 0.556800 0.438700 H -0.825800 0.574700 0.432500 $end $rem EXCHANGE gen BASIS aug-cc-pvdz LRC_DFT true OMEGA 300 OMEGA_GDD true $end $xc_functional X wPBE 1.0 C PBE 1.0 $end