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Ab initio molecular orbital calculations (Hartree–Fock, HF and density functional theory, DFT) of the 17 O NMR electrical field gradient (EFG) parameters for the bridging oxygen (O B ) in the model cluster H 4 P 2 O 7 are presented. The variation of the quadrupolar coupling constant ( C Q ) and asymmetry parameter ( η Q ) for the EFG of the bridging oxygen was shown to be a function of both the bridging P–O B –P bond angle and the OP–O B –PO conformation. These ab initio calculations allowed empirical relationships between the 17 O NMR EFG parameters and the P–O B –P bond angle to be tabulated for a wide range of OP–O B –PO conformations. For experimentally realistic ranges of the P–O B –P bond angle, the 17 O NMR EFG parameters are dominated by variations in the P–O B –P bond angle, with minor changes due to the OP–O B –PO conformation. These calculations also demonstrated systematic differences in the predicted 17 O EFG parameters obtained using HF and DFT level of theory.