%0 Journal Article %1 hlwoodcock:Lopez1996 %A Lopez, X. %A Ugalde, J. M. %A Sarasola, C. %A Cossio, F. P. %D 1996 %J CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE %K bibtex-import %N 6 %P 1032--1048 %T On the accuracy of density functional theory for ion-molecule clusters. A case study of PL(n)(+) clusters of the first and second row hydrides %V 74 %X PL(n)(+) clusters (n = 1, 2 and L = NH3, OH2, FH, PH3, SH2, ClH) in both their triplet and singlet states have been characterized by common approximate density functional methods, SVWN, BVWN, BLYP, and B3LYP. The phosphorus-ligand distances (R), dissociation energies (D-0), triplet-singlet gaps (Delta(t-s)), and several bond properties, such as the electron density (rho(r(c))), the Laplacian (del(2) rho(r(c))), and the local energy density H(r(c)) at the bond critical point, were compared with those obtained by accurate ab initio molecular orbital theory, namely, second-order Moller-Plesset (MP2) and G2 theory. In general, it is observed that the local spin density approximation (SVWN) yields stronger bonds than ab initio molecular orbital theory. However, addition of gradient corrections to the exchange functional (BVWN) yields ion-molecule bonds that are too weak. Finally, taking account also of gradient corrections to the correlation functional (BLYP) leads to very close agreement with ab initio results. Among these functionals, Becke's hybrid functional, B3LYP, best fit the second-order Moller-Plesset and G2 data, reproducing the qualitative trends observed for the above-mentioned properties of phosphorus clusters, except for del(2) rho(r(c)). This fit is particularly good for distances, dissociation energies, and electron densities at the bond critical point, and both methods show similar deviations of the values of binding energies and triplet-singlet gap with respect to the G2 data. Compared with our most accurate ab initio molecular orbital data, namely G2, significant overbinding for the singlets, larger for one-ligand than for two-ligand complexes, and significant overestimation of the triplet-singlet gap for one-ligand complexes is observed for both methods, namely, B3LYP and MP2. The deviations at the second-order Moller-Plesset level of theory are mainly due to the lack of quadratic configuration interaction (QCI) corrections, and this deficiency is also present to some extent in B3LYP. However, for larger clusters these corrections are smaller, therefore the B3LYP functional is expected to lead to accurate descriptions.

@article{hlwoodcock:Lopez1996, abstract = {PL(n)(+) clusters (n = 1, 2 and L = NH3, OH2, FH, PH3, SH2, ClH) in both their triplet and singlet states have been characterized by common approximate density functional methods, SVWN, BVWN, BLYP, and B3LYP. The phosphorus-ligand distances (R), dissociation energies (D-0), triplet-singlet gaps (Delta(t-s)), and several bond properties, such as the electron density (rho(r(c))), the Laplacian (del(2) rho(r(c))), and the local energy density H(r(c)) at the bond critical point, were compared with those obtained by accurate ab initio molecular orbital theory, namely, second-order Moller-Plesset (MP2) and G2 theory. In general, it is observed that the local spin density approximation (SVWN) yields stronger bonds than ab initio molecular orbital theory. However, addition of gradient corrections to the exchange functional (BVWN) yields ion-molecule bonds that are too weak. Finally, taking account also of gradient corrections to the correlation functional (BLYP) leads to very close agreement with ab initio results. Among these functionals, Becke's hybrid functional, B3LYP, best fit the second-order Moller-Plesset and G2 data, reproducing the qualitative trends observed for the above-mentioned properties of phosphorus clusters, except for del(2) rho(r(c)). This fit is particularly good for distances, dissociation energies, and electron densities at the bond critical point, and both methods show similar deviations of the values of binding energies and triplet-singlet gap with respect to the G2 data. Compared with our most accurate ab initio molecular orbital data, namely G2, significant overbinding for the singlets, larger for one-ligand than for two-ligand complexes, and significant overestimation of the triplet-singlet gap for one-ligand complexes is observed for both methods, namely, B3LYP and MP2. The deviations at the second-order Moller-Plesset level of theory are mainly due to the lack of quadratic configuration interaction (QCI) corrections, and this deficiency is also present to some extent in B3LYP. However, for larger clusters these corrections are smaller, therefore the B3LYP functional is expected to lead to accurate descriptions.}, added-at = {2006-06-16T05:03:46.000+0200}, author = {Lopez, X. and Ugalde, J. M. and Sarasola, C. and Cossio, F. P.}, biburl = {https://www.bibsonomy.org/bibtex/23f6b835486e6d2033067c0b83a0480f7/hlwoodcock}, citeulike-article-id = {569867}, interhash = {888eaeaf7e933e4e2621b3ca0fed7e9b}, intrahash = {3f6b835486e6d2033067c0b83a0480f7}, journal = {CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE}, keywords = {bibtex-import}, number = 6, pages = {1032--1048}, priority = {2}, timestamp = {2006-06-16T05:03:46.000+0200}, title = {On the accuracy of density functional theory for ion-molecule clusters. A case study of PL(n)(+) clusters of the first and second row hydrides}, volume = 74, year = 1996 }