ELSEVIER 14 April 1995 Chemical Physics Letters 236 (1995) 206-210 CHEMICAL PHYSICS LETTERS Theoretical investigation of cis-nitric oxide dimer with hybrid density functional theory methods Branko S. Jursic Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA Received 10 January 1995 Abstract Hybrid density functional theory (DFF) has been applied to a model geometry and derived bonding energy of cis-nitric oxide dimer. The obtained results were compared with ab initio RHF and MP2, SVWN and BLYP DFT and experimental data. The basis sets used ranged from small (3-21G *) to large (6-311 + + G(3df)). The suitability of DFT hybrid methods for modeling this system is discussed. 1. Introduction Density functional theory (DFT) [1] is becoming an increasingly popular tool for predicting the prop- erties of chemicals of interest [2,3]. The exorbitant cost of high accuracy ab initio calculations has in- creased the attractiveness of the more economical Kohn-Sham [4] DFF approach. Recently, we per- formed a computational study of the NO dimer structure with density functional theory localized and nonlocalized methods [5]. The quality of the obtained results depends on the basis sets used. It was esti- mated that with 6-311 + G(2d) satisfactory results could be obtained. Localized DFT methods give slightly improved results over RHF, while nonlocal- ized DFT methods produce results that are close to ab initio MP2 or even MP3 calculations. Our study of the further application of DFT methods for the modeling of ab initio problematic structures, such as FNNF [6] and FSSF [7], reveal that hybrid methods produce structures much closer to experimental val- ues. This was also the case with all the C-H com- pounds in a study of Diels-Alder reactions using butadiene and cyclopentadiene as dienes and ethy- lene as dienophile [8]. The structures of the reactants were best fitted with hybrid methods and the activa- tion energies predicted with BECKE3LYP and BECKE3P86 were about 1-2 kcal/mol away from experimental values and the quality that can be obtained by ab initio MP4 energy evaluation on MP2 geometries. The structure of nitric oxide dimer is especially interesting for computational modeling be- cause the long weak N-N bond (2.33 A) is hard to predict correctly. In our previous work [5] we considered the trans- nitric dimer and NO monomer, here we will study only the cis-ONNO isomer and any reference to the NO dimer should be understood as being cis. The NO dimer binding energy consists of a van der Waals complex with ground state which is a singlet. Thus three electrons of the two open-shell NO monomers are coupled in ON-NO. The structure of the NO dimer has been exten- sively studied experimentally. There are many results that are quite different, and there is still dispute as to what is the actual structure. An X-ray crystallo- 0009-2614/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0009-2614(95)00200-6