Jichong Wei

Rules of pair electron correlation in MF(M=H, Li, Na)

In this paper, the transferable property of pair correlation energies of F centered orbitals is discussed for a series F containing compounds MF(M=H, Li, Na). Comparing our two calculated results using 6-311++G(d) and cc-PV5Z* basis sets, it is found that the absolute values of the correlation energy of these systems increase with the increase of the size of the basis set, but the following relative changing regularities remain the same. In F containing compounds, from F neutral atom through HF, LiF, NaF to F−, both the intra-, interpair correlation energies and intra-, intershell correlation energies of the inner orbital electrons differ little. The correlation effects of 1sF2 are very much alike in all the above F containing systems and such pair correlation is transferable. However, the valence intrapair correlation and intrashell correlation energies are large and differ a lot in all systems. In MF molecules, the F correlation energy contribution increases with the increase of the ionic bond strength ...

Estimating electron correlation energies of A2 from A− and A+ ionic units with a simple scaling approach

Electron pair correlation contribution from individual electron pairs of the molecular orbitals is defined and used in analyzing the correlation patterns of F2, O22−, and CH3CH3 isoelectronic covalent systems. Based on our simple strategy so-called “separating large system into smaller ones” for estimating the correlation energies by investigating both the ionic and the diradical partitioning schemes for covalent systems, a simple scaling scheme is presented for estimating the total correlation energy. It is achieved by summing the scaled correlation energies of its ionic fragments derived from the ionic partitioning scheme rather than from the diradical partitioning scheme. Of the three estimated results, the absolute deviations are less than ±0.29 kcal/mol, however, using this simple scaling approach, at least 90% of computational work can be saved. At the present condition with the computational demand for calculating the electron correlation energies of large covalent molecules, it is hopeful that thi...

Rapid estimation of the electronic correlation energies for van der Waals complexes

Abstract We present the rules of calculations of pair electron correlation energies for Rg(Ne, He), X (X=F, Cl, Br) and the corresponding van der Waals complexes RgX at MP2/6-311++G(d) level and He, Ne, HeF and NeF with larger cc-PV5Z* basis set using ROHF-OPT2 method of meld program. The analyses from the aspects of pair correlation energies, charge distributions and orbital coefficients indicate that the correlation effects between Rg and atom X in the RgX systems are very small. Comparing the results of electron correlation energies between RgX and Rg+X, we propose a rapid approximation estimation method to estimate the correlation energies for van der Waals complexes by directly summarizing the correlation energies of Rg and X systems.

The correcting method for the estimation of correlation energies of MF2 (M = Be, Mg, Ca) set molecules

The intrapair and interpair correlation energies of MF2 (M = Be, Mg, Ca) set molecules are calculated and analysed, and the transferability of inner core correlation effects of Mδ+ are investigated. A detailed analysis of the comparison of correlation energies of neutral atoms with their corresponding ions of Mδ+ and Fδ/2 is given in terms of the correlation contribution of this component. The study reveals that the total correlation energy of MF2 molecules can be obtained by summing the correlation contributions of Mδ+ and two Fδ-/2 components. This simple estimation method does shed light on the importance of searching useful means for the calculation of electron correlation energy for large biological systems.

Approach to estimate correlation energies of MNO3 (M = Li, Na, K) molecules

Abstract According to the pair correlation energy results of MNO 3 (M=Li, Na, K) at MP2-OPT2/6-311++G(d) level with M eld program and the transferability of pair correlation energies of M δ + and NO 3 δ − in MNO 3 molecules, a simple approach to estimate correlation energy of MNO 3 is reported which can save a lot of computation time. The total correlation energy of MNO 3 at MP2(full)/6-311++G(d) and MP2(full)/6-311++G(3df, 3pd) levels by G aussian 94 procedure are also given in order to compare with those of M eld results and to discuss the influence of basis set size both on the calculation of correlation energy and on the presented simple approach.