Effective small core

Relativistic effective small-core core potentials with triple-zeta... 

Relativistic effective small-core core potentials with triple-zeta valence orbitals augmented by two sets of polarization functions were used for Sn and Pb. 

The effect of core-electron correlation is small, as shown in Table 11.16. It should be noted that the valence and core correlation energy per electron pair is of the same magnitude, however, the core correlation is almost constant over the whole energy surface and consequently contributes very little to properties depending on relative energies, like vibrational frequencies. It should be noted that relativistic corrections for the frequencies are expected to be of the order of 1 cm" or less. ... 

Previously derived results for the charge-density profile and polarization profile in this model solution, valid only for small fields, were used. Although these did not consider the penetration of the electrons into the solution, the change in the field is small. A Harrison-type pseudopotential84 was used to represent the effect of core electrons of the solution species on the metal electrons. 

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]. 

The present work represents a preliminary attempt to incorporate many of these strategies in conjunction with the use of small-core relativistic effective core potentials for obtaining compact series of correlation consistent basis sets... 

To be small and effective, a core team should have around twelve members. For major, high-priority projects each team member must have considerable authority and responsibility within their respective functional organization. Each team member... 

Use of the SBKJC and CRENBL ECPs appear to be less prevalent in the current literature. The SBKJC ECP, also called the consistent effective potential (CEP), developed by Stevens and coworkers is also large core. The CRENBL ECP developed by La John and coworkers is small core, where the 10 4d electrons are also classified as valence electrons, leaving 36 electrons to be treated as core electrons in the ECP. 

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