NMR lineshape in Metallic Nanoparticles: a Matrix Continued Fraction evaluation

In metallic nanoparticles, the different electronic environment seen by each magnetic nucleus produces a distribution of Knight shifts of the NMR frequencies which is observed as an inhomogeneously broadened lineshape. We study the fluctuations in the local density of states for s electrons at the Fermi energy in a simple LCAO model. We resort to a Matrix Continued Fractions calculation of the Green's functions. Results show that line broadens asymmetrically and its shift decreases as the particle size or the temperature diminish satisfying a universal scaling function. However, for very small particles, surface states become relevant to determine a lineshape that departs from the universal scaling behavior. These trends are consistent with the observed tendencies in Cu and Pt particles.