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Optimised auxiliary basis sets for lanthanide atoms (Ce to Lu) for four basis sets of the Karlsruhe error-balanced segmented contracted def2 - series (SVP, TZVP, TZVPP and QZVPP) are reported. These auxiliary basis sets enable the use of the resolution-of-the-identity (RI) approximation in post Hartree-Fock methods - as for example, second-order perturbation theory (MP2) and coupled cluster (CC) theory. The auxiliary basis sets are tested on an enlarged set of about a hundred molecules where the test criterion is the size of the RI error in MP2 calculations. Our tests also show that the same auxiliary basis sets can be used together with different effective core potentials. With these auxiliary basis set calculations of MP2 and CC quality can now be performed efficiently on medium-sized molecules containing lanthanides. [ABSTRACT FROM AUTHOR]

A systematic way to construct compact complementary auxiliary basis sets (ABSs) from and for atomic natural orbital basis sets for the use as resolution-of-the-identity sets in explicitly correlated F12 calculations is presented. The performance of these newly constructed ABSs has been benchmarked in explicitly correlated calculations of absolute energies, ionisation potentials and electron affinities. [ABSTRACT FROM PUBLISHER]

Abstract: High-level quantum-chemical calculations are reported at the MP2 and CCSD(T) levels of theory for the equilibrium structure and the harmonic and anharmonic force fields of diacetylene, Hh name="tbnd" />Ch name="tbnd" />Clculations were performed employing Dunning’s hierarchy of correlation-consistent basis sets cc-pVXZ, cc-pCVXZ, and cc-pwCVXZ, as well as the ANO2 basis set of Almlöf and Taylor. An empirical equilibrium structure based on experimental rotational constants for 13 isotopic species of diacetylene and computed zero-point vibrational corrections is determined and in good agreement with the best theoretical structure (CCSD(T)/cc-pCV5Z: , , ). In addition, the computed fundamental vibrational frequencies are compared with the available experimental data and found in satisfactory agreement. [Copyright &y& Elsevier]

Abstract: Seven ortho rotational transitions have been recorded for the main isotopic species of water in the millimeter- and submillimeter-wave region using the Lamb-dip technique in order to resolve the hyperfine structure due to the hydrogens and to provide accurate hyperfine constants. The experimental determination has been supplemented by high-level quantum-chemical calculations of the hyperfine parameters thereby focusing in particular on a systematic study of the basis-set convergence and on vibrational effects. [Copyright &y& Elsevier]