  The thermodynamic mixing properties of alkali feldspar solid solutions
between the Na and K end members were computed through atomistic simulations
using a neural network potential. We performed combined molecular dynamics and
Monte Carlo simulations in the semi-grand canonical ensemble at 800 {\deg}C and
considered three quenched disorder states in the Al-Si-O framework ranging from
fully ordered to fully disordered. The excess Gibbs energy of mixing, excess
enthalpy of mixing and excess entropy of mixing are in good agreement with
literature data. In particular, the notion that increasing disorder in the
Al-Si-O framework correlates with increasing ideality of Na-K mixing is
successfully predicted. Finally, a recently proposed short range ordering of Na
and K in the alkali sublattice is observed, which may be considered as a
precursor to exsolution lamellae, a characteristic phenomenon in alkali
feldspar of intermediate composition leading to perthite formation during
cooling.
