Precision Hybrid Density Functional Method

We have presented a novel LHDC-DFT method,which combines highly accurate WFT methods with low-cost DFT methods,to compute the energy and electronic structure of medium and large molecules.The method requires one to divide an entire system into small subsystems and to optimize the local hybrid coefficientηof a hybrid DFT functional for each subsystem according to the energy of the subsystem calculated by a high level WFT method. Further refinement to r/(local hybrid coefficient) is made by incorporating couplings between the subsystems.The new set of local hybrid coefficients is then used to calculate the energy and electronic structure of the entire system with the hybrid DFT functional.The new method can accurately reproduce the energy profiles of the highly accurate WFT methods.Since for small subsystems,highly accurate WFT methods can be applied,our LHDC method provides a route to systematically converge DFT results to "exact" results for medium and large molecules which are too large to be calculated with the accurate WFT methods.The cost of the LHDC method equals the cost of a usual DFT calculation for the entire system plus additional efforts to obtain the local hybrid coefficients.Our results indicate that a second-order LHDC method which is just slightly more expensive than a DFT method can already give satisfactory results on potential energy profiles for highly delocalized systems such as fully conjugated alkenes.From a WFT view point,our method is a DC method using DFT as "glue" to bind subsystems but with the capability of reproducing the WFT energy and providing electronic structure information for the entire system that is not addressed by conventional EDC methods. From a DFT view point,the hybrid coefficients of subsystems(local regions) are optimized according to the energy of the accurate WFT method,and thus our method can be viewed as a new local hybrid DFT method.³⁸ Thus the "local hybrid(LH)" in the name LHDC has double meaning,the hybrid of DFT and WFT through the optimization of local hybrid coefficientηof the DFT exchange.