Ab initio ground‐state potential energy function and vibration‐rotation energy levels of imidogen,NH

The accurate ground‐state potential energy function of imidogen, NH, has been determined from ab initio calculations using the multireference averaged coupled‐pair functional (MR‐ACPF) method in conjunction with the correlation‐consistent core‐valence basis sets up to octuple‐zeta quality. The importance of several effects, including electron correlation beyond the MR‐ACPF level of approximation, the scalar relativistic, adiabatic, and nonadiabatic corrections were discussed. Along with the large one‐particle basis set, all of these effects were found to be crucial to attain “spectroscopic” accuracy of the theoretical predictions of vibration‐rotation energy levels of NH. © 2015 Wiley Periodicals, Inc.