An improved long-range corrected hybrid exchange-correlation functional including a short-range Gaussian attenuation (LCgau-BOP)

A new hybrid exchange- correlation functional is presented based on the long- range correction (LC) scheme [H. Iikura et al., J. Chem. Phys. 115, 3540 (2001); Tawada et al., J. Chem. Phys. 120, 8425 (2004)], named LCgau- BOP. The key feature is the use of a two- parameter Gaussian correction to the Coulomb attenuation, which allows a more flexible description of exact exchange at short- range interelectronic separations. The new partitioning preserves 100% exact exchange in the long range, which is known to be important for the success of the LC scheme, with an asymptotic attenuation described by a standard error function with a parameter of 0.42. The LCgau partitioning was optimized for the reproduction of atomization energies over the G2 set and reaction barrier heights over Database/ 3, and produced results which are superior to B3LYP, CAM- BLYP, and the best LC functionals we are aware of. The results highlight the importance of including a substantial portion of exact exchange in the short range. Using the same parameters, the new functional was tested for the reproduction of geometries, as well as valence, Rydberg and charge- transfer excitations which are known challenges for conventional density functional theory. Our conclusion is that LCgau- BOP can provide a consistently more accurate description of thermochemistries, chemical reactions, and excitation energies than other existing long- range corrected functionals. (C) 2007 American Institute of Physics. [DOI: 10.1063/ 1.2790017]