A molecular dynamics calculation of solid phase of malonic acid: role of hydrogen-bond chains and the elastic constants

Abstract

Recent studies suggest that hydrogen bonds, in particular, hydrogen bond chains play an important role in determining the properties of a substance. We report an investigation into the triclinic phase of crystalline malonic acid. One of two intermolecular interaction potentials proposed here is seen to predict the lattice parameters as well as the enthalpy of the triclinic phase in good agreement with experimental data. Structural and dynamic properties are reported. Also reported are the lifetime of the hydrogen bond and hydrogen bond chains of length l along [011] direction where l = 1 to 5. From the temperature dependence of the lifetime we have obtained the activation energies of the chains. We also report the elements of elastic constant tensor. The results show that the presence of the hydrogen bond chain along [011] direction leads to higher value for elastic tensor $$\hbox {C}_{yyzz}$$ suggesting a strong correlation between hydrogen bond chains and the elastic constant along that direction. This is consistent with the recent report of Azuri I et al. 2015 Angew. Chem. Int. Ed. Engl. 54 13566 who reported that rather large Young’s modulus for certain amino acid crystals. The calculation reports the lifetime and activation energies of hydrogen bond chains and demonstrates that there is a relation between direction of the hydrogen bond chains and elastic constants along that direction. Presence of hydrogen bonds along a given crystallographic direction leads to larger elastic constants. A view down the a direction. Cyan dots represent centre of mass of malonic acid molecule in the triclinic crystal phase and red lines indicate hydrogen bond between them. Note the existence of hydrogen bond chains along [011] direction.