The equilibrium N-H bond length

The equilibrium structures of NH3, NH2F, NHF2, NF3, HNC, HNO, HN3, HNCO, an d NH4+ were calculated at the CCSD(T) level of theory with basis sets of at least quadruple zeta quality and with a correction for the core correlatio n calculated with the cc-pCVQZ basis set. Then, the possibility of calculat ing accurate ab initio N-H bond lengths is examined using a sample of 13 mo lecules whose equilibrium structures are known. Three different correlated methods are compared: CCSD(T), MP2, and DFT using the hybrid functional B3L YP. As expected, the CCSD(T)/cc-pVQZ method gives the most accurate results but, except for HNO, the MP2/6-31G** and B3LYP/6-311++G(3df,2pd) methods a re also satisfactory, their standard deviation being smaller than 0.002 Ang strom provided a small offset correction is taken into account. (C) 2000 Pu blished by Elsevier Science B.V.