Affiliations: [a] Institut de Química Computacional and Departament de Química, Universitat de Girona, Campus Montilivi, 17071 Girona, Spain | [b] Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain | [c] Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling, Vrije Universiteit Amsterdam, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Abstract: We report here a study into what causes the dramatic differences between OPBE and PBE for reaction barriers, spin-state energies, hydrogen-bonding and π - π stacking energies. It is achieved by the implementation of a new functional that switches smoothly from OPBE to PBE at a predefined point P of the reduced density gradient s. By letting the point P run as function of the reduced density gradient s, with values from s = 0.1 to s = 10, we can determine which part of the exchange functional determines its behavior for the different interactions. Based on the thus obtained results, we have created a new exchange functional that shows the good results of OPBE for reaction barriers and spin-state energies, and combines it with the good respectively reasonable results of PBE for hydrogen-bonding and π - π stacking. In summary, the new functional combines the best of OPBE with the best of PBE.
