On the choice of gaussian 4f functions for use in calculations on transition metal compounds

One uncontracted 4f gaussian function is found to perform well as a polarization function at the SCF level When correlation is included, it is found that a two-gaussian fit to a Slater 4f function is much superior to a single gaussian, but that a three-term GTO fit is only slightly better than the two-term GTO 4f.     

The sensitivity of B3LYP atomization energies to the basis set and a comparison of basis set requirements for CCSD(T) and B3LYP

The atomization energies of the 55 G2 molecules are computed using the B3LYP approach with a variety of basis sets. The 6–311 + G(3df) basis set is found to yield superior results to those obtained using the augumented-correlation-consistent valence-polarized triple-zeta set. The atomization energy of SO₂ is found to be the most sensitive to basis set and is studied in detail. Including tight d functions is found to be important for obtaining good atomization energies. The results for SO₂ are compared with those obtained using the coupled-cluster singles and doubles approach including a perturbational estimate of the triple excitations.     

The atomic states of nickel

The Ni 3d ⁹ 4s ¹(³ D)–3d ¹⁰(¹ S) and 3d ⁹ 4s ¹(³ D)-3d ⁸4s ²(³ F) atomic excitation energies have been computed using large multireference CI wave functions in conjunction with a large ANO basis set. Radial correlation effects in the 3d shell are found to be very important and are included using CASSCF wave functions having the 3d and correlating 3d orbitals in the active space. The previous discrepancy (0.5 eV) with experiment for the ³ D–¹ S excitation is reduced to 0.1 eV when the 3d3d references are included in the CI. For the ³ F state, the 4s-4p near degeneracy gives rise to important 4s ²4p ² excitations in addition to the 3d3d excitations which are important for the ³ D and ¹ S states. Inclusion of only 3d-3d correlation in the ³ F and ³ D CI reference spaces yields a ³ F–³ D separation which is in error by 0.12 eV. Addition of the 4s ²4p ² excitations to the ³ F reference space is estimated to increase the discrepancy with experiment by an additional 0.1 eV.     

Theoretical study of the first transition row oxides and sulfides

Summary The first transition row oxides and sulfides are studied using several different levels of theory. The calculations show the bonding mechanism in the sulfides and oxides to be very similar. For the oxides, accurate experimental data allow the theoretical methods to be calibrated. The same level of theory is used to study the sulfides where there is far less experimental information. For ScO through MnO and CuO the coupled cluster singles and doubles technique including a perturbational estimate of the connected triple excitations [CCSD(T)] yields spectroscopic constants (_e, _e, andD ₀) in good agreement with experiment. The triple excitations are found to be very important in achieving this accuracy. For FeO to NiO, the self-consistent-field (SCF) approach yields orbitals that are localized on the metal or oxygen. This appears to cause problems for the single reference techniques; this is discussed in detail for NiO. The complete-active-space SCF/internally contracted averaged coupled pair functional approach (CASSCF/ICACPF) works well for FeO to NiO. The calculation of accurate dipole moments is found to be very difficult.     

The electron affinities of transition metal atoms at the CCSD(T) and density functional levels of theory

 The electron affinities of Ti, V, Cr, Fe, Co, Ni, and Cu are computed using the density function theory and CCSD(T) approaches. Overall the CCSD(T) approach yields the best results. For this property, the B3LYP, BLYP, and BP86 functionals perform better than the BPW91, PBEPBE, and PBE1PBE ones. The accuracy of all the methods is higher if the number of 3delectrons is the same in the neutral atom and the anion. This is especially true for the density functional theory methods. Received: 23 January 2002 / Accepted: 1 April 2002 / Published online: 24 June 2002     

Computation of electronic transition moments: the length versus the velocity representation

Summary We have compared transition moments (TMs) obtained using the length and velocity representations for transitions from the ground state of H₂ to the lowest two¹ _u and two¹ _u ⁺ Rydberg states, theA ¹–X ¹⁺ transition in BH, and theA ¹ _u –X ¹ _g ⁺ transition in C₂. For H₂, the TMs in the length and velocity representations agree well even in cases where the one-particle basis is incomplete and the TM has not converged. For BH and C₂ the TM in the length representation converges rapidly with improvements in the one-particle basis set and is insensitive to inner-shell correlation. In contrast, in the velocity representation convergence with improvements in the one-particle basis is much slower, especially for C₂, and the TMs are significantly changed by inner-shell correlation. Thus the difference between the TMs in the length and velocity representations would not appear to be a viable diagnostic of TM convergence.     

A challenge for density functional theory: the XONO and XNO2 (X=F, Cl, and Br) molecules

The equilibrium geometries, harmonic frequencies, dipole moments, infrared intensities, and relative energies of the cis-XONO, trans-XONO, and XNO₂ (X=F, Cl, and Br) have been investigated using four functionals in common use in Kohn-Sham density functional theory (DFT) calculations. Two of the functionals include non-local or gradient correction terms, while the other two also incorporate some exact Hartree-Fock exchange and are labeled hybrid functionals. The quality of the results obtained from the functionals is determined by comparison to previously published high-level coupled-cluster calculations. The hybrid functionals perform better for prediction of the equilibrium geometries, where the two gradient corrected functionals yield qualitatively incorrect molecular structures for cis-FONO and cis-ClONO. None of the functionals perform well in predicting all six harmonic frequencies, showing that the correlation between equilibrium geometries and harmonic frequencies is not as strong for these DFT methods as it is for conventional wavefunction ab initio methods, such as coupled-cluster theory. Results from the various functionals generally come into better agreement with each other and also with the coupled-cluster results moving down the periodic table. Received: 12 February 1997 / Accepted: 25 March 1997     

The vibrational frequencies of CaO2, ScO2, and TiO2: a comparison of theoretical methods

The vibrational frequencies of several states of␣CaO₂, ScO₂, and TiO₂ are computed using density functional theory (DFT), the Hartree-Fock approach, second-order M?ller-Plesset perturbation theory (MP2), and the complete-active-space self-consistent-field theory. Three different functionals are used in the DFT calculations, including two hybrid functionals. The coupled cluster singles and doubles approach including the effect of connected triples, determined using perturbation theory, is applied to selected states. The Becke-Perdew 86 functional appears to be the most cost-effective method of choice, although even this functional does not perform well for one state of CaO₂. The MP2 approach is significantly inferior to the DFT approaches. Received: 3 September 1997 / Accepted: 8 December 1997     

Convergence of the binding energy of oxygen on Cu(100): A cautionary tale for computational chemists using periodic bound conditions

The convergence of the binding energy of oxygen on Cu(100) as a function of the k‐points, energy cutoff for the inclusion of plane waves, surface model, and oxygen coverage is studied. Overall the convergence is good, with an accuracy of 0.1 eV obtained for an affordable level of treatment. Published 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009