Effective core potentials coupled-cluster

The only calculation we found for CdH is the work of Balasubramanian [68], using Cl with relativistic effective core potentials. The coupled-cluster results are presened in Table 6. Calculated values for R , cOg and Dg agree very well with experiment. Relativity contracts the bond by 0.04 and reduces the binding energy by 0.16 eV. The one- and two-component DK method reproduce the relativistic effects closely. Similar trends are observed for the excited states (Tables 7-9). Comparison with experiment is difficult for these states, since many of the experimental values are based on incomplete or uncertain data [65]. Calculated results for the CdH anion are shown in Table 10. The... 

In Table 6.3, the values of De for RfCU are compared with those obtained within various approximations using relativistic effective core potentials (RECP) Kramers-restricted Hartree-Fock (KRHF) (Han et al 1999), averaged RECP including second-order M0ller-Plesset perturbation theory (AREP-MP2) for the correlation part (Han et al. 1999), RECP coupled-cluster single double (triple) [CCSD(T)] excitations (Han et al. 1999), and a Dirac-Fock-Breit (DFB) method (Malli and Styszynski 1998). The AREP-MP2 calculation of De gives 20.4 eV, while the RECP-CCSD(T) method with correlation leads to 18.8 eV. Our value of De of 19.5 eV is just between these calculated values. 

By ab initio we refer to quantum chemical methods in which all the integrals of the theory, be it variational or perturbative, are exactly evaluated. The level of theory then refers to the type of theory employed. Common levels of theory would include Hartree-Fock, or molecular orbital theory, configuration interaction (Cl) theory, perturbation theory (PT), coupled-cluster theory (CC, or coupled-perturbed many-electron theory, CPMET), etc. - We will use the word model to designate approximations to the Hamiltonian. For example, the zero differential overlap models can be applied at any level of theory. The distinction between semiempirical and ab initio quantum chemistry is often not clean. Basis sets, for example, are empirical in nature, as are effective core potentials. The search for basis set parameters is not usually considered to render a model empirical, whereas the search for parameters in effective core potentials is so considered. 

High-level theoretical calculations included ab initio relativistic effective core potentials (RECP) with MP2, MP4 and coupled-cluster methods, which emphasised the importance of elecfronic correlation in the correct description of fhe compounds (Di Bella ef al., 1996). This initial study was further refined by ab initio mefhods (Hong ef al., 1999) and relativistic DPT calculations (Dolg, 2001 Hong et al., 1999,2000 Lu and Li, 1999) The most recent calculations seem to favour an s d rafher fhan fhe f —> d promotion scheme in the metal-ligand bonding of fhe zero-valenf complexes. 

AIMD = ab initio molecular dynamics B-LYP = Becke-Lee-Yang-Parr CCSD = coupled cluster single double excitations CVC = core-valence correlation ECP = effective core potential DF = density functional GDA = gradient corrected density approximation MCLR = multiconfigurational linear response MP2 = M0ller-Plesset second-order (MRD)CI = multi-reference double-excitation configuration interaction RPA = random phase approximation TD-MCSCF = time-dependent multiconfigurational self-consistent field TD-SCF = time-dependent self-consistent field. 

MRCI, CCSD(T), and DMRG) compared to the choice of the one-electron Hamiltonian (DKH and effective core potential) with a special emphasis on the order of the DKH Hamiltonian. The calculated results are compared to data from experiment. The effect of the one-particle basis set can be seen for CsH from the entries for the contracted bases of quality [lls9pSd] and [Ils9p8rf2/1 ], respectively. Note also the importance of the approximation for the total wave function (as, for example, highlighted in the case of SnO for uncomelated Dirac-Hartree-Fock or even nonrelativistic Hartree-Fock compared to the coupled-cluster results). 

Han, Y.-K., Hirao, K. Two-component coupled-cluster calculations for the hydride of element 111 on the performance of relativistic effective core potentials. Chem. Phys. Lett. 328, 453 58 (2000)... 

Coupled-cluster Theory Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Relativistic Effective Core Potential Techniques for Molecules Containing Very Heavy Atoms Relativistic Theory and Applications. 

Basis Sets Correlation Consistent Sets Benchmark Studies on Small Molecules Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Configuration Interaction PCI-X and Applications Core-Valence Correlation Effects Coupled-cbister Theory Density Functional Applications Density Functional Theory (DFT), Har-tree-Fock (HF), and the Self-consistent Field Density Functional Theory Applications to Transition Metal Problems Electronic Structure of Meted and Mixed Nonstoi-chiometric Clusters G2 Theory Gradient Theory Heats of Formation Hybrid Methods Metal Complexes Relativistic Effective Core Potential Techniques for Molecules Containing Very Heavy Atoms Relativistic Theory and Applications Semiempiriced Methetds Transition Metals Surface Chemi-ced Bond Transition Meted Chemistry. 

The ionization potentials and electron affinities of the atoms H, C, N, O and F have been computed by means of coupled-cluster methods using doubly augmented correlation-consistent one-electron basis sets in conjunction with explicitly correlated Slater-type geminals. Excitations up to the level of connected quintuples have been accounted for, and all orbitals in the core and valence shells have been correlated. Relativistic effects (spin-orbit as well as scalar) and diagonal Born-Oppenheimer corrections have been included. 

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