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We present CASPT2 calculations of vertical excitation energies for low‐lying singlet and triplet states of auroderivatives of acetylene and ethylene representing small model aurocarbons. Data are supplemented by CCSD(T) results for triplet states. All four considered species, namely linear C2Au2 molecule and three conformers of the C2Au4 molecule—Au2C2Au2 (tetraauroethylene, the analog of the parent ethylene molecule) and σ– and π–adducts of the Au2 molecule with the auroacetylene exhibit considerable lowering of low‐lying excitation energies when compared with their parent acetylene and ethylene molecules. Singlet and triplet excitation energies of diauroacetylene drop by 57% and 48%, respectively, and of tetraauroethylene, by 68% and 56% when compared with their respective parent molecules. Even more is lowered the singlet–triplet energy gap. We stress the importance of the dynamical correlation in CASPT2 calculations and discuss problems with selection of the appropriate active space in aurocarbons. [ABSTRACT FROM AUTHOR]

Spectroscopic and electric properties of the series of diatomic molecules FCu, FAg and FAu are calculated using the coupled cluster method, taking into consideration the relativistic effects of the no-pair one-component Douglas-Kroll-Hess approximation. The correlation and relativistic effects in the FM series (M = Cu, Ag, Au) are compared with these effects in the AlM series. Differences in the bonding character and molecular properties in FM and AIM are primarily due to different relativistic effects in both series.

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Interaction energies between the coinage metal atoms (Cu, Ag, and Au) and lone-pair donating molecules (H[sub 2]O and NH[sub 3]) are calculated by the spin adapted restricted open-shell Hartree–Fock coupled cluster method with the scalar relativistic effects accounted for by the Douglas–Kroll approximation. All ammonia complexes CuNH[sub 3], AgNH[sub 3], and AuNH[sub 3] are found to be of C[sub 3v] symmetry with the counterpoise corrected interaction energies equal to -16.68, -6.87, and -14.64 mH for Cu, Ag, and Au, respectively. In the case of the water molecule the complexes are much weaker with the counterpoise corrected interaction energies equal to -3.78, -1.81, and -1.77 mH, for the three metal atoms, respectively. Moreover, all complexes with the water molecule are nonplanar. For both lone-pair donating molecules the structure and energetics of their complexes with the coinage metal atoms is mostly due to electron correlation effects. The relativistic effects are found to increase the bonding energies in the series of the ammonia complexes, whereas they reduce the bonding energy in the AgOH[sub 2] complex and are essentially negligible for CuOH[sub 2] and AuOH[sub 2]. The calculated complex geometries and interaction energies are discussed in terms of different models. The pattern of interaction energies is discussed in terms of the balance between long-range induction and dispersion contributions and short-range forces. Also the possibility of some charge transfer from the lone-pair donor to the metal atom is considered and supported by analysis of the ionization potential and electron affinity data. The relativistic reduction of the size of the coinage metal atoms is found to be of importance as well. The calculated structural data are used to interpret the experimental observation concerning the existence of well resolved resonantly enhanced multiphoton ionization (REMPI) spectra of the ammonia–silver complexes and the absence of the corresponding spectra of the water–silver complex. This experimental difference between the ammonia and water complexes is explained in terms of the very flat interaction energy function for the wagging motion of the water molecule in AgOH[sub 2]. This large amplitude vibration makes the structure of the complex undefined and is responsible for the nonexistence of the vibrationally resolved REMPI spectrum of the complex.© 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The article discusses a new approach, wherein the virtual orbital space (OVOS) technique is optimized to conduct more efficient coupled cluster, CCSD(T) calculations of the intermolecular interactions taking place in the model hydrogen-bonded and stacked dimers. The technique is shown to be extremely effective in minimizing the errors that are caused while calculating the interaction energies.

The electronic and structural properties of the Cu...S[H.sub.2], Ag...S[H.sub.2] and Au...S[H.sub.2] complexes are examining by using the spin-adapted restricted open-shell HF coupled cluster CCSD(T) method combined with the second-order spin-free Douglas-Kroll-Hess (DKH) relativistic approach. Relativistic changes of the metal element affinity and polarizability have helped in understanding major trends in the pattern of interactions between the coinage metal atoms and different lone pair donating ligands.