Hay-Wadt ECPs

Popular pseudopotentials in modem use include those of Hay and Wadt (sometimes also called the Los Alamos National Laboratory (or LANE) ECPs Hay and Wadt 1985), those of Stevens et al. (1992), and the Stuttgart-Dresden pseudopotentials developed by Dolg and co-workers (2002). The Hay-Wadt ECPs are non-relativistic for the first row of transition metals while most others are not as relativistic effects are usually quite small for this region of the periodic table, the distinction is not particularly important. Lovallo and Klobukowski (2003) have recently provided additional sets of both relativistic and non-relativistic ECPs for these metals. Eor the p block elements. Check et al. (2001) have optimized polarization and diffuse functions to be used in conjunction with the LANE double-t basis set. 

Hay and Wadt (1985a, b) have published ECPs which are in form identical to the averaged RECPs of Christiansen, Ermler and co-workers. However, there are differences. First, the Hay-Wadt potentials are derived from the Cowan-GriflSn adaptation of the Breit-Pauli Hamiltonian into a variational computation of the atomic wave-function. From these solutions the ECPs are generated. It should be noted that the spin-orbit coupling is not included in the Hay-Wadt ECPs. Consequently, molecular calculations done using these ECPs would not include spin-orbit coupling. 

For accurate calculations of TM compounds, f-type polarization functions should be added to the basis set. Exponents for f-polarization functions have been optimized by us for the Hay-Wadt ECP. No other sets of f-type functions optimized for use with pseudopotentials are known to us. However, because the valence orbitals of the pseudopotentials mimic the all-electron orbitals, the f-type functions determined for all-electron cases can also be used for pseudopotential calculations. 

Now we discuss calculated bond dissociation energies. The Stoll-Preuss ECPs proved to be clearly superior to the Hay-Wadt ECPs for this project, so... 

The other known EGP and valence-electron basis sets were generated using the procedure, described for Hay-Wadt ECP generation. Durand-Barthelat large-core semilocal ECP [484] and corresponding valence-electron basis sets are generated for 3d-transition elements and the main-group elements Li to Kr. 

LACVP basis sets use 6-3IG for main group elements and the Hay-Wadt ECP for Ni Hay PJ, Wadt WR (1985) J Chem Phys 82 299... 

Four basis sets were examined BSl and BS3 are based on the Couty-Hall modification of the Hay and Wadt ECP, and BS2 and BS4 are based on the Stuttgart ECP. Two basis sets, BSl and BS2, are used to optimize the geometries of species in the OA reaction, [CpIr(PH3)(CH3)]++ CH4 [CpIr(PH3)(H)(CH3)2]+, at the B3LYP level, while the other basis sets, BS3 and BS4, are used only to calculate energies at the previously optimized B3LYP/BS1 geometries. BSl is double-zeta with polarization functions on every atom except the metal atom. BS2 is triple-zeta with polarization on metal and double-zeta correlation consistent basis set (with polarization functions) on other atoms. BS3 is similar to BSl but is triple-zeta with polarization on the metal. BS4 is similar to BS2 but is triple-zeta with polarization on the C and H that are involved in the reaction. The basis set details are described in the Computational Details section at the end of this chapter. 

Slovenia), using the DFT implementation in the Gaussian03 code. Revision C.02 (8). The orbitals were described by a mixed basis set. A fully uncontracted basis set from LANL2DZ was used for the valence electrons of Re (9), augmented by two / functions Q =1.14 and 0.40) in the full optimization. Re core electrons were treated by the Hay-Wadt relativistic effective core potential (ECP) given by the standard LANL2 parameter set (electron-electron and nucleus-electron). The 6-3IG basis set was used to describe the rest of the system. The B3PW91 density functional was used in all calculations. 

Owing to computational limitations, the model used to represent the first shell of CA was the (NH3)3M (H20) system. This complex has been widely used in ab initio calculations of different mechanistic aspects of the CA enzyme [31]. Furthermore, the validity of this model, where the three imidazole ligands are substituted by three ammonia groups, has been previously assessed [31e, 32]. In the present study, full geometry optimizations of all eight minima with no symmetry constraints were performed. Pseudopotential wave functions have been preferred to full-electron calculations, because valence Similarity can be more easily related to reactivity than all-electron Similarity [33]. Dunning s valence double zeta quality basis set [34] together with the Hay and Wadt ECPs... 

Figure 2 Plot of Cl—Cl distance versus relative total energy of CI2 for all-electron (AE) and ECPs of Hay-Wadt (HW), Kahn-Baybutt-Truhlar (KBT), and Christiansen-Lee-Pitzer (CLP). ...

Initially, the level of theory that provides accurate geometries and bond energies of TM compounds, yet allows calculations on medium-sized molecules to be performed with reasonable time and CPU resources, had to be determined. Systematic investigations of effective core potentials (ECPs) with different valence basis sets led us to propose a standard level of theory for calculations on TM elements, namely ECPs with valence basis sets of a DZP quality [9, 10]. The small-core ECPs by Hay and Wadt [11] has been chosen, where the original valence basis sets (55/5/N) were decontracted to (441/2111/N-11) withN = 5,4, and 3, for the first-, second-, and third-row TM elements, respectively. The ECPs of the second and third TM rows include scalar relativistic effects while the first-row ECPs are nonrelativistic [11], For main-group elements, either 6-31G(d) [12-16] all electron basis set or, for the heavier elements, ECPs with equivalent (31/31/1) valence basis sets [17] have been employed. This combination has become our standard basis set II, which is used in a majority of our calculations [18]. 

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