The nuclear quadrupole moment of N-14 from accurate electric field gradient calculations and microwave spectra of NP molecule

Extensive series of relativistic coupled cluster calculations of the electric field gradient at N in NP has been carried out. The accurate value of the calculated electric field gradient, combined with the highly accurate experimental value of the nuclear quadrupole coupling constant for the N-14 nucleus, gives the 'molecular' value of the nuclear quadrupole moment Q(N-14) = 20.46 mb. This result perfectly agrees with the value (20.44 +/- 0.03 mb) determined from atomic calculations and atomic spectra. The present study involves also extensive investigations of basis sets which must be used in highly accurate calculations of electric field gradients.