Full Theoretical Model Research Articles

The electron density distribution in the hydrogen bond. A quantum chemical and crystallographic study

With the help of Hartree—Fock—Slater calculations in which very large basis sets are employed, the polarisation of the water molecule by an electric field is explored. The various features in the electron density distribution are encountered again in the long hydrogen bond in the water dimer, showing that polarisation is the main effect. In short hydrogen bonds, exchange repulsion is shown to be equally important. The quality of the computational method is tested by comparing the results of the calculation of the electron density distribution in the crystal of α-oxalic acid dihydrate with the results of accurate X-ray diffraction measurements. By using models in which subsequently covalent bonding, hydrogen bonding and the electrostatic crystalline field are included, the effects of the various components are explored. Only the full theoretical model gives excellent agreement with the experiment, showing the quality of the model and the sensitivity of the experiment.

An induction gradiometer for conductivity contrast detection: Theoretical considerations

We present a full wave theoretical model for an induction gradiometric sensor employed for detection of conductivity contrast. The sensor is composed of a wire antenna radiating from a rectangular waveguide, with receivers in the waveguide positioned symmetrically on either side of the transmitter. We first solve the canonical problem of an open‐ended rectangular waveguide in a planar stratified medium and then apply reciprocity and the Born approximation to deduce the response of the sensor in the presence of an arbitrary external medium. We compare our results against experimentally measured data and find excellent agreement. We present a discussion of these results together with an analysis of the numerical considerations involved in the computation.