Second‐order elastic constants of hexagonal hydroxylapatite (P63) from ab initio quantum mechanics: Comparison between DFT functionals and basis sets

• Published in: International journal of quantum chemistry 2018-03, Vol.118 (5), p.n/a
• Main Authors: Ulian, Gianfranco, Valdrè, Giovanni
• Format: Article
• Language: English
• Subjects: Chemistry; Constants; Density functional theory; elastic constants; Elastic properties; GTO and PW basis sets; Hamiltonian functions; Hydroxyapatite; hydroxylapatite; Modulus of elasticity; Physical chemistry; Plane waves; Quantum mechanics; Quantum theory
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.25500

Three very popular Hamiltonians in the density functional theory framework, PBE, PBEsol, and B3LYP, and different basis sets (Gaussian‐type orbitals and plane waves) were employed to simulate the hydroxylapatite unit cell and its second‐order elastic constants. Dispersive interactions were included in the quantum‐mechanical treatment via the DFT‐D2 and Tkatchenko‐Scheffler schemes. The calculated bulk, shear, and Young's moduli were in the range of 82‐117 GPa, 42‐51 GPa, and 107‐134 GPa, respectively. The axial moduli, Ka and Kb, were instead in the range of 277‐322 GPa and 506‐509 GPa. The theoretical data, especially those from plan waves simulations, are in good agreement with available results in literature and further extend the knowledge of the mechanical and vibrational properties of hydroxylapatite. Ab initio DFT methods are of common use to investigate mechanical properties of increasingly complex solid phases. In this work, a thorough comparison between several computational approaches (GTO and PW basis sets, DFT Hamiltonians, inclusion of dispersive forces) in describing the second‐order elastic constants of hydroxylapatite is reported, aiming to help the interested researchers in modelling the mechanical properties of this solid phase or similar systems.