| Abstract
| - The dipole (hyper)polarizability of the copper dimer has been obtained from conventional ab initio and densityfunctional theory calculations. A very large (23s16p12d6f) basis set consisting of 346 Gaussian-type functionsis thought to provide reference results of near-Hartree−Fock quality for all properties. We obtain ᾱ = 102.54and Δα = 41.89 for the mean and the anisotropy of the dipole polarizability (ααβ/e2a02Eh-1). For the Cartesiancomponents and the mean of the hyperpolarizability (10-3γαβγδ/e4a04Eh-3) we obtain γzzzz = 309, γxxxx = 209,γxxzz = 87, and γ̄ = 244. Electron correlation lowers ᾱ but increases considerably Δα. The effect on thehyperpolarizability is enormous, as the longitudinal component γzzzz is drastically reduced, while γxxxx andγxxzz are nearly halved. At the CCSD(T) level of theory with a [7s6p6d2f] basis set we obtain ᾱ = 93.82, Δα= 67.09 and γzzzz = 18, γxxxx = 101, γxxzz = 35, and γ̄ = 86. The dipole polarizability varies as [ᾱ(R) −ᾱ(Re)]/e2a02Eh-1 = 28.09(R − Re) + 4.69(R − Re)2 − 0.52(R − Re)3 − 0.36(R − Re)4 and [Δα(R) − Δα(Re)]/e2a02Eh-1 = 49.58(R − Re) + 11.92(R − Re)2 − 1.94(R − Re)3 −1.32(R − Re)4 around the experimentalbond length Re = 2.2197 Å. B3LYP density functional theory calculations with a [8s7p7d5f] basis set yieldᾱ = 77.62, Δα = 44.73e2a02Eh-1, and γ̄ = (95.9 × 103)e4a04Eh-3. These values differ from the conventionalab initio results. The present investigation shows that the longitudinal component and the mean of thehyperpolarizability are positive around Re, in conflict with previous findings. The extension of (hyper)polarizability calculations to higher copper clusters is highly nontrivial and will require the development ofnew computational strategies.
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