Order and Disorder in Calcium Oxalate Monohydrate: Insights from First-Principles Calculations

Calcium oxalate minerals are broadly present in nature. They form through biogenic, geogenic, and pathogenic processes that lead to different pseudopolymorphs. Being the most common solid phase in human nephrolithiasis, calcium oxalate monohydrate (COM) in particular has been the focus of much investigation. It exists in several crystalline forms, two of which appear to be of biological and medical relevance: the low- and high-temperature forms (COM-LT and COM-HT, respectively). While there is broad consensus on the ordered structure of COM-LT, which possesses the P21/n space group symmetry, for COM-HT controversy remains. Experimental results suggest that there is a certain degree of structural disorder in the high-temperature form. However, the exact character of disorder in COM-HT is yet an open question. Here, we examine the effect of the disorder of water molecules on the structure of COM using first-principles calculations based on dispersion-augmented density functional theory (DFT). Such calculati...