Articles you may be interested inComparisons of results from parametrized configuration interaction (PCI80) and from hybrid density functional theory with experiments for first row transition metal compounds A recently suggested scheme termed parametrized configuration interaction with parameter X ͑PCI-X͒ for scaling the correlation energy has been applied on a benchmark test consisting of 32 first row molecules. Several different methods like Mo "ller-Plesset second-order perturbation theory ͑MP2͒, modified coupled pair functional method ͑MCPF͒, averaged coupled pair functional method ͑ACPF͒, coupled cluster singles and doubles ͑CCSD͒, and CCSD with a perturbational estimate of triple excitations ͓CCSD͑T͔͒ have been tested using systematically chosen basis sets ranging from double zeta ͑DZ͒ to very large atomic natural orbital ͑ANO͒ sets containing several sets of d and f functions. For each method and basis set the scaling parameter is optimized. The scaling does in all cases lead to large, sometimes dramatic, improvements of the results. Typically, using a single reference state method like MCPF the average absolute deviation compared to experiments for the benchmark goes from an unscaled value of about 20 kcal/mol down to about 2 kcal/mol. For MCPF and similar methods no improvement of the results is obtained going beyond the DZϩpolarization ͑DZP͒ level. Significant improvements due to scaling occurs even at the highest level using the CCSD͑T͒ method and the largest basis set. For medium size basis sets the present scaling is far superior to the extrapolation schemes used in the Gaussian-1 and -2 ͑G1 and G2͒ theories.

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Abstract. Two different cluster models mimicking bulk zinc oxide have been developed and tested. The goal has been to incorporate both the ionic and the covalent effects which are present in the bonding between zinc and oxygen. In the first model, termed the dipole model, the building units are neutral ZnO molecules. The binding within this unit is allowed to have covalent contributions, but the binding between different units is assumed to have only small covalent contributions. In the second model, termed the covalent model, the covalent character of the bonding between zinc and oxygen is emphasized. The building units are one-dimensional covalently bound chains of ZnO units. The dangling bonds in these chains are closed by adding hydrogen atoms and/or copper atoms. Both the dipole and the covalent model of zinc oxide give results for the bandgap which are at most in qualitative agreement with experimental measurements. For these models to be useful as quantitative tools in the future, further development is needed.