ANO basis

Atomic natural orbital (ANO) basis sets [44] are fonned by contracting Gaussian fiinctions so as to reproduce the natural orbitals obtained from correlated (usually using a configuration interaction with... 

There are several types of basis functions listed below. Over the past several decades, most basis sets have been optimized to describe individual atoms at the EIF level of theory. These basis sets work very well, although not optimally, for other types of calculations. The atomic natural orbital, ANO, basis sets use primitive exponents from older EIF basis sets with coefficients obtained from the natural orbitals of correlated atom calculations to give a basis that is a bit better for correlated calculations. The correlation-consistent basis sets have been completely optimized for use with correlated calculations. Compared to ANO basis sets, correlation consistent sets give a comparable accuracy with significantly fewer primitives and thus require less CPU time. 

The smaller cluster ions 83", 84" and 85 + have been examined by Zakrzewski and von Niessen at the HF/6-3H-G level [82]. The lowest cationic states are predicted to be 82, and A" for 83 (Cyv), 84 (I>4h) and (Cs), respectively. The ionisation processes may result in significant structural relaxation leading to the sequence of states different from that of the vertical states. The calculated lowest adiabatic ionisation energies, using the GI method with a very large ANO basis set, are 9.53, 8.05, and 8.20 eV for 83, 84 and 85 , respectively. 

At the highly correlated CASSCF-AQCC level of conventional ab initio theory using a very large [7s6p4d3f2g] ANO basis set. 

Main Group Atoms and Dimers Studied with a New Relativistic ANO Basis Set. 

New Relativistic ANO Basis Sets for Transition Metal Atoms. 

Calculations of ionization energies and electron affinities were performed with a modified development version of Gaussian 99 [48], Pople and Effective Core Potential (ECP) basis sets are provided in this software [49], Dunning and Atomic Natural Orbital (ANO) basis sets were obtained from the EMSL Gaussian Basis Set Library [50],... 

Among the ANO basis sets, the Roos double-C basis set is clearly preferable. Convergence problems were encountered with Roos triple-C basis sets, especially during the pole search in the propagator calculation. Preliminary results are encouraging. 

Finally, I can compare my SCF and CAS results with corresponding rotational London orbital calculations by Ruud and co-workers [32-36,61]. My SCF results for HF using the vD + D basis set and conventional or rotational London orbitals are almost identical to a rotational London orbital result 0.7627 using the daug-cc-pVQZ basis set [34,61] or a result 0.7626 obtained with a large ANO basis set [34,35]. Similarly the 1000 54220 iooO(. 5633i jjp... 

Almlof, J., Taylor, P.R. Atomic natural orbital (ANO) basis-sets for quantum-chemical calculations. Adv. Quantum Chem. 1991, 22, 301-73. 

Pierloot, K., Dumez, B., Widmark, P.-O., Roos, B.O. Density-matrix averaged atomic natural orbital (ANO) basis-sets for correlated molecular wave-functions. IV. Medium-size basis-sets for the atoms H-Kr. Theor. Chim. Acta 1995, 90, 87-114. 

Table 5.2 shows the N2 dissociation energy obtained with a sequence of ANO basis sets at the MRCI level [68]. We should note that all ten valence electrons are correlated in these calculations, which are based on a six-electron six active orbital CASSCF reference. 

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