The compressional behaviour and the mechanical properties of talc [Mg3Si4O10(OH)2]: a density functional theory investigation

Int J of Quantum Chemistry

2017

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Hydroxylapatite is an important calcium phosphate phase whose knowledge is useful in different fields, for instance in bone biology, development of biomaterials and even cultural heritage. In this work, the equation of state of this mineral was calculated by using the quasi-harmonic approximation, also including for the first time the temperature effect. In athermal conditions (0 K), we found that the pressure dependence of the hydroxylapatite unit cell volume is well described by a third-order Birch-Murnaghan formulation, with parameters K 0 5 115.9(1), K' 5 4.47(6), and V 0 5 524.323 (27). The inclusion of temperature led to a lower bulk modulus, for example, KT 0 5 109.55 GPa at 300 K. The thermal expansion coefficient between 0 and 1000 K was also reported. The results are in good agreement with the few available experimental data reported in literature and further extend the knowledge of the mechanical and thermal behavior of this important mineral. K E Y W O R D S DFT/B3LYP-D*, equation of state, hydroxylapatite, quasi-harmonic approximation, thermal expansion coefficient | I N TR ODU C TI ONThe growing interest in biomaterials and biominerals led, in recent years, to several researches aimed to unravel the mechanical properties of calcium phosphates among which hydroxylapatite (OHAp, space group P6 3 /m, Figure 1) is one of the most investigated because of its similarities to the mineral phase of bone and dental tissues. For instance, specific and peculiar experimental Raman piezo-spectroscopy were employed to better understand the microscopic processes governing the behavior of natural bone tissues (sane and osteoporotic) as well as the mechanochemical framework describing how the microstructure of synthetic biomaterials affects the failure of artificial joints. [1,2] This method can analyse the mechanical stress as stored in the apatite crystals belonging to both natural bone (sane and osteoporotic) and synthetic biomaterials by the Raman shift of the apatite (compared to unstressed apatite). Another example regards the mechanical stability and failure of hydroxylapatite/collagen fibrils nano-composite, which was simulated by molecular mechanics methods in several works of Dubey and Tomar. [3][4][5] Finally, the effects of carbonate ion on the OHAp unit cell was studied from both the structural [6][7][8][9][10] and vibrational [11][12][13][14] points of view, to better understand the differences between stoichiometric hydroxylapatite and biological apatite (which contains several CO 22 3 and other ionic substitutions). Hexagonal OHAp is known to be a piezoelectric material, a property related to the ordered hydroxyl group alignment in the calcium channel.According to recent studies in literature, [15][16][17][18] OHAp exhibits also a ferroelectric behavior. Being a piezoelectric compound, a detailed knowledge on the mechanical properties of hydroxylapatite could be important.Hydroxylapatite is also a valued material for cultural heritage purposes. Recently, it was found that this mineral could be used to...

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Section: Resultsmentioning

confidence: 99%

{normalΓ}_{tot} = 22 A + 22 B + 22 E_{1} + 22 E_{2}

where A and B modes do not present degeneracies and E modes are doubly degenerated.…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Equation of state of hexagonal hydroxylapatite (P6₃) as obtained from density functional theory simulations

Int J of Quantum Chemistry

2017

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“…This particular DFT method is called B3LYP‐D*. The same approach has been adopted with good results in previous works on phyllosilicates, where dispersive forces are dominant …”

Section: Methodsmentioning

confidence: 99%

“…For further details on the ELASTCON approach, we suggest the reader to refer to the work of Perger and coworkers . The algorithm was used with good results in the calculation of the thermochemical‐physical properties of BaTiO 3 , rutile TiO 2 and talc . To ease the comparison between the two QM codes, we considered for each required unit cell deformation a three‐points displacement (NUMDERIV = 3 in CRYSTAL, NFREE = 2 in VASP) with a step of 0.015 Å (STEP and POTIM keywords in CRYSTAL and VASP, respectively).…”

Section: Methodsmentioning

confidence: 99%

Second‐order elastic constants of hexagonal hydroxylapatite (P6₃) fromab initioquantum mechanics: Comparison between DFT functionals and basis sets

Int J of Quantum Chemistry

2017

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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.

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Density functional investigation of the thermophysical and thermochemical properties of talc [Mg3Si4O10(OH)2]

2014

Phys Chem Minerals