Electronic structure methods B3LYP functional

A comment is due regarding the performance of different electronic structure methods for cluster systems. For covalently bound molecules, the available spectroscopic evidence indicates, as was noted above, that the accuracy of the DFT B3LYP and B97 functionals roughly matches that of MP2. For hydrogen-bonded clusters, comparisons that can be made for systems such as (H20) and C1 (H20), (by using the results of Refs. [93,94,103, 104]), show that MP2 is in better accord with experiment than DFT. Such comparisons can be viewed as a spectroscopic test as to which potential surface is more accurate. 

Common language of electronic structure theory, validating density functional theory, standardization of Gaussian basis sets, semiempirical methods, B3LYP functional (Becke s three-parameter hybrid functional using the LYP correlation functional), well-defined procedures for QM algorithms... 

The basis set is 6-31G(d,p), and electron correlation at the MP2 level is included. A similar structure is obtained with the AMI and PM3 semi-empirical methods. Density functional theory at the B3LYP/6-31G(dp,p) level also produced the same structure for this ion-pair. The only observed differences between the semi-empiri-cal and the ab initio structures were slightly shorter hydrogen bonds (PM3 and AMI) between FI, F2, and F5 and the G2-F1 (H18) on the imidazolium ring. 

The electronic structure calculations were carried out using the hybrid density functional method B3LYP [15] as implemented in the GAUSSIAN-94 package [16], in conjunction with the Stevens-Basch-Krauss (SBK) [17] effective core potential (ECP) (a relativistic ECP for Zr atom) and the standard 4-31G, CEP-31 and (8s8p6d/4s4p3d) basis sets for the H, (C, P and N), and Zr atoms, respectively. 

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