Electron-correlation calculation

HypcrChcrn sup )orLs MP2 (second order Mollcr-Plessct) correlation cn crgy calculation s tisin g ah initio rn cth ods with an y ava liable basis set. In order lo save mam memory and disk space, the Hyper-Chern MP2 electron correlation calculation normally uses a so called frozen -core" appro.xiniatioii, i.e. the in n er sh ell (core) orbitals are om it ted,. A sett in g in CHKM. INI allows excitation s from the core orbitals lo be included if necessary (melted core). Only the single poin t calcii lation is available for this option. ... 

Eleig, T. and Visscher, L. (2005) Large-scale electron correlation calculations in the framework of the spin-free dirac formalism the Au2 molecule revisited. Chemical Physics, 311, 63. 

Ab initio electron correlated calculations of the equilibrium geometries, dipole moments, and static dipole polarizabilities were reported for oxadiazoles <1996JPC8752>. The various measures of delocalization in the five-membered heteroaromatic compounds were obtained from MO calculations at the HF/6-31G level and the application of natural bond orbital analysis and natural resonance theory. The hydrogen transfer and aromatic energies of these compounds were also calculated. These were compared to the relative ranking of aromaticity reported by J. P. Bean from a principal component analysis of other measures of aromaticity <1998JOC2497>. 

Next, we assess the roie of the eiectron correiation. We performed the electron correlation calculations at two levels the UHF and MP2. The comparison of these results with the calculation at the ROHF level allows to study the influence of the electron correlation with the different allowance of the latter. 

Duncanson and Coulson [242,243] carried out early work on atoms. Since then, the momentum densities of aU the atoms in the periodic table have been studied within the framework of the Hartree-Fock model, and for some smaller atoms with electron-correlated wavefunctions. There have been several tabulations of Jo q), and asymptotic expansion coefficients for atoms [187,244—251] with Hartree-Fock-Roothaan wavefunctions. These tables have been superseded by purely numerical Hartree-Fock calculations that do not depend on basis sets [232,235,252,253]. There have also been several reports of electron-correlated calculations of momentum densities, Compton profiles, and momentum moments for He [236,240,254-257], Li [197,237,240,258], Be [238,240,258, 259], B through F [240,258,260], Ne [239,240,258,261], and Na through Ar [258]. Schmider et al. [262] studied the spin momentum density in the lithium atom. A review of Mendelsohn and Smith [12] remains a good source of information on comparison of the Compton profiles of the rare-gas atoms with experiment, and on relativistic effects. 

Gauss has derived shielding theory with electron correlated calculations in the Moller-Plesset expansion (43,44) and also in the coupled cluster approach (45). He has provided benchmark calculations on a set of small molecules shown in Tables II and III at the CCSD(T) level (46). 

We have calculated the data presented in the table in collaboration with G. V. Smeloy (Kaplan et al., 1983, 1985). In the MO LCAO approximation we have used the same bases of atomic functions as in calculations of the excitation probabilities of the corresponding molecules (see Section III,B,1). Allowing for electron correlation, calculations of the number of Cl configurations and the atomic bases were the same as those given in Section III,B,2. 

Since 1986 there have been quite a few electron-correlated calculations of y(Ne), usually based on many-body perturbation theory. However, the results have been chopping and changing (see Table 2) due to basis set size and the care with which various... 

Wells, B. H. and Wilson, S., van der Wools interaction potentials. Basis set superposition effects in electron correlation calculations. Mol. Phys. 50, 1295-1309 (1983). 

We see that DFT is increasingly used to model a wide range of weak interactions in protein-ligand and nucleic acid-ligand systems. Often, DFT is the only method that can incorporate all electron correlated calculations and that can be applied in... 

A major advantage of DFT theory is its relatively low computational intensity compared with post-afc initio electron correlation calculations.21 Because DFT calculations can be augmented with empirical data relevant to the transition metals, they are now the preferred approach to theoretical studies of organotransi-tion metal chemistry. We must point out, however, that theoreticians still cannot know ahead of time which DFT method will work best for a particular situation ... 

B. H. Wells and S. Wilson, Mol. Phys., 50, 1295 (1983). Van der Waals Interaction Potentials. Basis Set Superposition Effects in Electron Correlation Calculations. See also. Mol. Phys., 54,787... 

For the AtH molecule, the two-component results are in good agreement with the DC results of Visscher et al. [73] at the correlated level of theory. Among the DC results, the aug-pVDZ results are closer to the REP results than the aug-pVTZ results, partially reflecting the basis set quality of the REP calculations. For the (117)H molecule, the REP-KRHF results are in reasonable agreement with the all-electron DHF results of Saue et al. [74]. There are no reports of all-electron correlation calculations for (117)H. Electron correlation effects... 

Instead, Nicolaides and Beck [37b, p. 506] considered the exactly solvable problems of the harmonic oscillator and of hydrogen and found that in fact, a single function can diagonalize H(rd ). This is the rotated function of the unrotated solution, i.e., [H(rd ) — e ] (rd ) = 0, for each state n > and real e . (The proof is straight-forward). In fact, we stated two "theorems" that are basic to the development of the practical implementation of the CESE-SSA [37b, p. 505], since, in practice, they allow the difficult electron correlation calculations to be done only once on the real axis, and then continue the computation in the complex energy plane where the Gamow orbitals are optimized until the complex energy is stabilized. 

The differences that are noted above imply that if an electron-correlation calculation were carried out using the same basis sets for the wavefunc-tions of these two spectroscopic terms, then the size requirements would be very large, simply in order to correct for the inadequacy of the zero-order wavefunctions. 

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