Divergences of the single reference perturbation theories due to the addition of diffusion basis functions have been investigated for both closed-shell and open-shell molecular systems. It is found that the oscillator...Divergences of the single reference perturbation theories due to the addition of diffusion basis functions have been investigated for both closed-shell and open-shell molecular systems. It is found that the oscillatory range of perturbation energies of open-shell systems increases as the spin multiplicity of systems changes from 2 to 4. Feenberg transformation is exploited to treat the divergence problems. It is found numerically that within the interval of Feenberg parameter there exists a minimum perturbation order at which the perturbation series become convergent. It is also found for the open-shell systems that the magnitude of the corresponding Feenberg parameter becomes larger as the spin multiplicity of the system of interest changes from 2 to 4.展开更多
Iterative multireference configuration interaction (IMRCI) is proposed. It is exploited to compute the electronic energies of H2O and CH2(singlet and triplet states) at equilibrium and non-equilibrium geometries. The ...Iterative multireference configuration interaction (IMRCI) is proposed. It is exploited to compute the electronic energies of H2O and CH2(singlet and triplet states) at equilibrium and non-equilibrium geometries. The potential energy curves of H2O, CH2(singlet and triplet states) and N2 have also been calculated with IMRCI as well as the M?ller Plesset perturbation theory (MP2, MP3, and MP4), the coupled cluster method with single and double substitutions (CCSD), and CCSD with perturbative triples correction (CCSD(T)).These calculations demonstrate that IMRCI results are independent of the initial guess of configuration functions in the reference space and converge quickly to the results of the full configuration interaction. The IMRCI errors relative to the full configuration interaction results are at the order of magnitude of 10-5 hartree within just 2-4 iterations. Further,IMRCI provides an efficient way to find on the potential energy surface the leading electron configurations which, as correct reference states, will be very helpful for the single-reference and multireference theoretical models to obtain accurate results.展开更多
基金the National Natural Science Foundation of China (No.21473008 and No.21873011).
文摘Divergences of the single reference perturbation theories due to the addition of diffusion basis functions have been investigated for both closed-shell and open-shell molecular systems. It is found that the oscillatory range of perturbation energies of open-shell systems increases as the spin multiplicity of systems changes from 2 to 4. Feenberg transformation is exploited to treat the divergence problems. It is found numerically that within the interval of Feenberg parameter there exists a minimum perturbation order at which the perturbation series become convergent. It is also found for the open-shell systems that the magnitude of the corresponding Feenberg parameter becomes larger as the spin multiplicity of the system of interest changes from 2 to 4.
基金supported by the National Natural Science Foundation of China(No.21473008 and No.21873011)
文摘Iterative multireference configuration interaction (IMRCI) is proposed. It is exploited to compute the electronic energies of H2O and CH2(singlet and triplet states) at equilibrium and non-equilibrium geometries. The potential energy curves of H2O, CH2(singlet and triplet states) and N2 have also been calculated with IMRCI as well as the M?ller Plesset perturbation theory (MP2, MP3, and MP4), the coupled cluster method with single and double substitutions (CCSD), and CCSD with perturbative triples correction (CCSD(T)).These calculations demonstrate that IMRCI results are independent of the initial guess of configuration functions in the reference space and converge quickly to the results of the full configuration interaction. The IMRCI errors relative to the full configuration interaction results are at the order of magnitude of 10-5 hartree within just 2-4 iterations. Further,IMRCI provides an efficient way to find on the potential energy surface the leading electron configurations which, as correct reference states, will be very helpful for the single-reference and multireference theoretical models to obtain accurate results.
