Addendum: anomalous mechanical behavior of the deltic, squaric and croconic cyclic oxocarbon acids

Abstract

The mechanical properties of the deltic, squaric, and croconic acids were determined in a previous work by using rigorous theoretical solid-state methods based in Density Functional Theory using plane waves and pseudopotentials using a high-quality setup. These three materials were shown to display small negative Poisson ratios (NPR). Croconic acid was also shown to exhibit the phenomenon of negative linear compressibility (NLC) for applied pressures larger than ∼0.4 GPa directed along the direction of minimum Poisson ratio. The main purpose of this communication is to show that the croconic acid also exhibits the NLC phenomenon when submitted to isotropic pressures. The a lattice parameter of croconic acid increases for applied isotropic pressures in the range from 0.41 GPa to 0.46 GPa. The computed compressibility along a direction at the pressure of P = 0.44 GPa is ka = −79.7 TPa−1.