Capability of X-ray diffraction to the determination of the macroscopic linear susceptibility in a crystalline environment: the case of 3-Methyl 4-Nitropyridine N-oxide (POM)

Effective molecular polarizabilities and crystal refractive indices estimated from x-ray diffraction data

“…[6][7][8][9] The discrepancies observed between these earlier results and theory are much larger than the error introduced by the neglect or approximation of the local field effects, hence further pursuit of a strategy using just the moments of an experimental charge density is not worthwhile. The following section discusses the approximations made in previous work and presents an alternative way of deriving the dipole polarizability, ␣, from x-ray diffraction data, one which involves the use of wave functions fitted to x-ray diffraction data.…”

“…The expressions used by Baert and co-workers 6,7 and Vergoten and co-workers 8,9 derive from results published some time ago, based on either standard perturbation theory 27,28 or variation-perturbation theory. [29][30][31] The focus in much of this earlier work was the computation from first principles of nonlinear optical susceptibilities in the lowfrequency limit for III-V semiconductors, using approximate valence orbitals for the atoms in the crystal, and it is important to appreciate that those approaches assumed twoelectron bonds in which the two valence electrons are uncorrelated with any other pair of valence electrons and described by an effective one-electron Hamiltonian.…”

“…Agreement between x-ray derived results and low-level theory is even worse for ␤, with differences of more than two orders of magnitude, and even opposite signs, obtained for many elements of the tensor. Largely because of this the conclusions in the most recent publication 8 have been more circumspect.…”

“…6,7 The initial compound investigated was N-͑4-nitrophenyl͒-͑L͒-prolinol ͑NPP͒, and the same approach has also been recently used in the analysis of x-ray data for 3-methyl-4-nitropyridine-N-oxide ͑POM͒. 8,9 Both compounds are technologically important materials with possible applications in optical communications and related sectors, and their linear optical and NLO properties have been the subject of a large number of experimental and theoretical investigations. The x-ray charge density studies initially claimed to provide "relatively good results for ␣," but close inspection of the results for both compounds reveals that many of the diagonal components of the dipole polarizability tensors estimated from the x-ray diffraction data differ by more than an order of magnitude from lowlevel theoretical results ͑semiempirical AM1 or PM3 finite field results͒.…”

The Role of Hydrogen Bond in Designing Molecular Optical Materials

“…Some time ago, Fkyerat et al [18,19] and Hamzaoui et al [20,21] proposed a correlation between the molecular first-order polarizability α and first hyperpolarizability β with, respectively, the quadrupole and octupole electrostatic moments, derivable from the X-ray experiments. However, application of this method to organic non-linear optical materials revealed that many components of α and β tensors, calculated from X-ray diffraction, differ by more than an order of magnitude from theoretical results.…”