DFT Calculations for Cu-, Ag-, and Au-Containing Molecules

Abstract

The physicochemical properties of a set of molecules containing Cu, Ag, or Au atoms were calculated using the GAUSSIAN program suite, with the purpose of investigating the various density functional theory (DFT) approaches for subsequent application in cluster calculations. The test set comprised the copper-based molecules CuH, CuO, CuS, Cu2, CuCl2 -, CuCH3, CuC2H2, Cu2(HCO2)4(H2O)2, and Cu6H6(PH3)6 and the silver and gold diatomics AgH, AgO, AgS, Ag2, AgCu, AuH, AuO, AuS, Au2, AuCu, and AuAg. The DFT methods used were SVWN, BLYP, and BPW91, together with the DFT hybrids B3LYP and B3PW91. The calculations were carried out with the basis sets LANL2MB, LANL2DZ, 3-21G, and 6-311G (when available). The properties calculated were the molecular geometry, vibrational frequencies, and dissociation energies. It was found that all the DFT-based methods, particularly when allied with the LANL2DZ basis set, produced results which are significantly closer to experimental values than those of the traditional Moller−Plesset (MP2) electron correlation method and which are also applicable to considerably larger molecules. Over the whole test set of molecules, the RMS errors of the four “BX” methods, in conjunction with LANL2DZ, were typically 3−4% for geometries, 6−8% for frequencies, and 10−16% for dissociation energies, with BPW91 and the popular B3LYP at the lower and upper ends of these ranges, respectively, and with the errors being overestimates and underestimates, respectively. The corresponding values for SVWN and MP2 were 2% and 6%, 12% and 12%, and 33% and 42%, with these errors typically being ± and +, + and −, and + and −, with + and − representing overestimates and underestimates, respectively. While the best bond lengths are produced by SVWN (a local spin density approximation), which is not uncommmon, this advantage over the gradient corrected (BX) methods is only slight, and the latter are markedly superior for frequencies and especially dissociation energies. Not supported by the present results are the notions that (all) pure DFT methods underestimate metal−ligand bond lengths and overestimate bond strengths and that hybrid methods are superior (and neither that DFT methods are overcorrelated). Testing on a subset of molecules with BPW91/LANL2DZ revealed no benefit in supplementing this basis set by the addition of diffuse functions, nor of the counterpoise correction. There appear to be specific incompatibilities with some method/basis set combinations, and even the continuing availability of 3-21G for these metals is questionable. Because of its accuracy and reliability, the combination BPW91/LANL2DZ is recommended for these noble-metal systems (and to extensions such as the cluster-model approach to adsorption of a molecule on a metal surface).

Binding Interactions and Raman Spectral Properties of Pyridine Interacting with Bimetallic Silver–Gold Clusters

“…The present B3LYP predictions of the adiabatic ionization potential, electron affinity, dissociation energy, and bond distance are 8.64 eV, 1.43 eV, 1.91 eV, and 2.599 , respectively, which are close to the corresponding experimental values of < 9.15 eV, 1.31 eV, 2.08 AE 0.1 eV, 2.53 [11,12] and comparable to those of previous DFT calculations. [11] It is also noted that these values are in between Figure 1.…”

“…For inorganic or organic molecules binding to the gold-silver clusters, the chemical bonding depends strongly on the property of the unoccupied orbital in the metallic cluster. [12,13] Mitric et al studied the catalytic oxidation of CO and O 2 adsorbed on mixed silver-gold clusters with respect to the role of CT in the catalytic activity of AgAu À . [2] Chretien et al studied the adsorption of propene on mixed gold-silver clusters.…”

Theoretical study on the structure and formation mechanism of [C6H5Mm]− (MAg, Au; m = 1–3)

“…The standard basis set 6‐311G(d, p) is used for C and H atoms while Lanl2dz ECP32 basis set is adopted for Ag and Au atoms. It has been shown that these theoretical methods are currently the most accurate and appropriate approach for studying the structure and energy of organo‐coinage metal molecules or the coinage metal cluster 33–38. All transition states are located without imposing any constraints during the geometry optimization process and are confirmed by one imaginary mode from vibrational analysis calculations.…”

Formation of Ag2, Au2 and AgAu particles on MgO(100): DFT study on the role of support-induced charge transfer in metal–metal interactions

“…Free Ag 2 , Au 2 and AgAu particles have been previously investigated by Legge et al [32] using different DFT functionals and Gaussian functions. This methodology predicts a Ag-Ag bond relatively weaker than Au-Au and Ag-Au, a fact in agreement with experimental measurements.…”