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The Cauchy moments are derived and implemented for the approximate triples model CC3 with the proper N7 scaling (where N denotes the number of basis functions). The Cauchy moments are calculated for the Ne, Ar, and Kr atoms using the hierarchy of the coupled-cluster models CCS, CC2, CCSD, CC3 and a large correlation-consistent basis sets augmented with diffuse functions. A detailed investigation of the one- and N-electron errors shows that the CC3 results have the accuracy comparable to the experimental results.

We present ab initio calculations of the optical rotation of S-propylene oxide in both gas phase and solution using the coupled cluster methodology combined with a dielectric continuum description of the solvent. The coupled cluster calculations are performed using the CCS, CC2, CCSD and CC3 methods. None of the presented gas phase results are in accord with the experimental sign of the optical rotation at 355 nm. Thereby, the experimental sign change between the gas phase and the cyclohexane solution optical rotation at 355 nm is not reproduced theoretically. The vibrational effects are considered to be significant and may be of crucial importance in order to bring accordance between the calculated and the experimentally established sign of the gas phase optical rotation at 355 nm.

The Cotton-Mouton effect (magnetic field induced linear birefringence) has been studied for neon and argon using state-of-the-art coupled cluster techniques. The coupled cluster singles, doubles and triples (CCSDT) approach has been used to obtain static benchmark results and the CC3 model with an approximate treatment of triple excitations to obtain frequency-dependent results. In the case of neon the effect of excitations beyond triples has also been estimated via coupled cluster calculations including quadruple excitations (CCSDTQ), pentuple excitations (CCSDTQP), etc. up to the full configuration-interaction level. The results obtained for the anisotropy of the hypermagnetizability Delta eta (omega), the molecular property that determines the magnetic field induced birefringence of spherically symmetric systems, are Delta eta =2.89 a.u. for neon and Delta eta = 24.7 a.u. for argon, with a negligible effect of frequency dispersion. For neon we could estimate an absolute error on Delta eta of 0.1 a.u. The accuracy of these results surpasses that of recently reported experimental data.

$K\ensuremath{\beta}\ensuremath{-}\mathrm{to}\ensuremath{-}K\ensuremath{\alpha}$ x-ray intensity ratios have been measured for all the $3d$ transition metals from titanium to copper, and the valence electronic structures of these metals have been determined by comparing the measured $K\ensuremath{\beta}\ensuremath{-}\mathrm{to}\ensuremath{-}K\ensuremath{\alpha}$ x-ray intensity ratios with the results of our multiconfiguration Dirac-Fock calculation. Our experimentally determined valence electronic structures for all the metals except V, Cr, and Mn are found to agree reasonably well with the results of augmented plane-wave (APW) band structure calculations. Our results for the valence electronic structure of V and Mn are found to be closer to the free atom values whereas the valence electronic structure of Cr is found to lie in between the valence electronic structure predicted by Compton profile studies and the one given by APW band structure calculations. The electron occupancies of $3d$ and $(4s,4p)$ states of V, Mn, and Cu are similar to free atom occupancies whereas for the other metals we find rearrangement of electrons between $3d$ and $(4s,4p)$ states of the metal with the transfer of electrons from $3d$ to $(4s,4p)$ states for Cr and from $(4s,4p)$ to $3d$ states in the case of Ti, Fe, Co, and Ni.

$K\ensuremath{\beta}\ensuremath{-}\mathrm{t}\mathrm{o}\ensuremath{-}K\ensuremath{\alpha}$ x-ray intensity ratios of Fe and Ni in pure metals and in ${\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}$ alloys $(x=0.20,$ 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV $\ensuremath{\gamma}$ rays from a 200 mCi ${}^{241}\mathrm{Am}$ point source to understand why the properties of the ${\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x} (x=0.2)$ alloy are distinct from other alloy compositions. The valence electronic structure of Fe and Ni in the samples has been evaluated by comparing the measured $K\ensuremath{\beta}\ensuremath{-}\mathrm{t}\mathrm{o}\ensuremath{-}K\ensuremath{\alpha}$ intensity ratios with the results of multiconfiguration Dirac-Fock calculations. Significant changes in the $3d$ electron population (with respect to the pure metal) are observed for Fe and Ni for certain alloy compositions. These changes can be explained by assuming rearrangement of electrons between $3d$ and $(4s,4p)$ band states of the individual metal atoms. It has been found that the valence electronic structure of the ${\mathrm{Fe}}_{0.2}{\mathrm{Ni}}_{0.8}$ alloy is totally different from the other two alloys, which perhaps is connected to the special magnetic properties of this alloy.

Relative $K$ x-ray intensities of $Mn$ in $Mn$, $MnO_{2}$, $LaMnO_{3}$ and $La_{0.7}B_{0.3}MnO_{3}$ ($B$ = $Ca$, $Sr$, and $Ce$) systems have been measured following excitation by 59.54 keV $\gamma$-rays from a 200 mCi $^{241}$Am point-source. The measured results for the compounds deviate significantly from the results of pure $Mn$. Comparison of the experimental data with the multiconfiguration Dirac-Fock (MCDF) effective atomic model calculations indicates reasonable agreement with the predictions of ionic model for the doped {manganites except} that the electron doped $La_{0.7}Ce_{0.3}MnO_{3}$ and hole doped $La_{0.7}Ca_{0.3}MnO_{3}$ compounds show some small deviations. The results of $MnO_{2}$ and $LaMnO_{3}$ deviate considerably from the predictions of the ionic model. Our measured $K\beta/K\alpha$ ratio of $Mn$ in $La_{0.7}Ca_{0.3}MnO_{3}$ cannot be explained as a linear superposition of $K\beta/K\alpha$ ratios of $Mn$ for the end members which is in contrast to the recent proposal by Tyson et al. from their $Mn$ $K\beta$ spectra., Comment: 14 pages, 4 figures. to appear in NIM-B.Please send an e-mail for figures

The basis-set convergence of cc-pVXZ basis sets is investigated for the MP2 and CCSD equilibrium bond distances and harmonic frequencies of BH, HF, CO, N-2, and F-2 by comparing with explicitly correlated R12 results. The convergence is, in general, smooth but slow-for example, for harmonic frequencies at the quadruple-zeta level, the basis-set error is typically 7 cm(-1); at the sixtuple-zeta level, it is about 2 cm(-1). For most constants, the convergence can be accelerated by using a two-point linear extrapolation procedure. Equilibrium bond distances, harmonic frequencies, anharmonic contributions, vibration-rotation interaction constants, and rotational constants for the vibrational ground state have been calculated for the same set of molecules using standard wave function and basis-set levels of ab initio theory. The accuracy of the calculated constants has been established by carrying out a statistical analysis of the deviations with respect to experiment. The largest errors for bond distances and harmonic frequencies calculated at the core-corrected CCSD(T)/cc-pV6Z level are 0.4 pm and 13.4 cm(-1), respectively. Much smaller errors occur for the anharmonic contributions. (C) 2003 American Institute of Physics.

The cluster perturbation series, CPS(D), for coupled cluster singles and doubles excitation energies is considered. It is demonstrated that the second-order model CPS(D-2) is identical to the configuration interaction singles with perturbative doubles, CIS(D) model. The third-order model, CPS(D-3), provides excitation energies of coupled cluster singles and doubles (CCSD) quality in the sense that the difference between CPS(D-3) and CCSD excitation energies is of the same size or smaller than the effect of adding triples corrections to CCSD excitation energies. We further show that the third-order corrections can be efficiently implemented, in particular, when the resolution of the identity approximation is used for integrals. We also show that the CPS(D-3) excitation energies can be determined for system sizes that are far beyond what can be considered in conventional CCSD excitation energy calculations. Published under license by AIP Publishing.