  We present a novel approach to reverse Monte Carlo (RMC) modeling,
SpecSwap-RMC, which makes use of pre-computed property data from a discrete
configuration space replacing atomistic moves with swap moves of contributions
to a sample-set representing the average, or summed property. The approach is
particularly suitable for disordered systems and properties which require
significant computer time to compute. We demonstrate the approach by fitting
jointly and separately the EXAFS signal and x-ray absorption spectrum (XAS) of
ice Ih using as SpecSwap sample-set 80 configurations from a space of 1382
local structures with associated pre-computed spectra. As an additional
demonstration we compare SpecSwap and FEFFIT fits of EXAFS data on crystalline
copper finding excellent agreement.
