“…The chemical shifts for C-13 have been calculated using wave function based methods such as MP2 [20][21][22], multiconfigurational self-consistent field (MCSCF) [22,23], CCSD [24,25], CCSD(T) [26], and coupled cluster theory with single, double, and triple excitations (CCSDT) [27,28]. However, the computational cost of those methods is so high, which prevents full application of those methods for routine simulations.…”