2005/12/01 by Fernando J. A. L. Cruz, José N. Canongia Lopes, Jorge C. G. Calado +1 · 46 citations
Materials Science · Chemistry · #Thermal and Kinetic Analysis #X-ray Diffraction in Crystallography #Crystallography and molecular interactions #Hexagonal crystal system #Molecular dynamics #Calcium #Materials science #Dynamics (music) #Chemical physics #Crystallography #Chemistry #Computational chemistry #Physics #Metallurgy
paper · doi:10.1021/jp054304p
published in The Journal of Physical Chemistry B 109(51), 24473-24479 (American Chemical Society)
openalex publication_date 2005/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/17
Structural and thermodynamic properties of crystal hexagonal calcium apatites, Ca10(PO4)6(X)2 (X = OH, F, Cl, Br), were investigated using an all-atom Born-Huggins-Mayer potential by a molecular dynamics technique. The accuracy of the model at room temperature and atmospheric pressure was checked against crystal structural data, with maximum deviations of ca. 4% for the haloapatites and 8% for hydroxyapatite. The standard molar lattice enthalpy, delta(lat)H298(o), of the apatites was calculated and compared with previously published experimental results, the agreement being better than 2%. The molar heat capacity at constant pressure, C(p,m), in the range 298-1298 K, was estimated from the plot of the molar enthalpy of the crystal as a function of temperature, H(m) = (H(m,298) - 298C(p,m)) + C(p,m)T, yielding C(p,m) = 694 +/- 68 J x mol(-1) x K(-1), C(p,m) = 646 +/- 26 J x mol(-1) x K(-1), C(p,m) = 530 +/- 34 J x mol(-1) x K(-1), and C(p,m) = 811 +/- 42 J x mol(-1) x K(-1) for hydroxy-, fluor-, chlor-, and bromapatite, respectively. High-pressure simulation runs, in the range 0.5-75 kbar, were performed in order to estimate the isothermal compressibility coefficient, kappaT, of those compounds. The deformation of the compressed solids is always elastically anisotropic, with BrAp exhibiting a markedly different behavior from those displayed by HOAp and ClAp. High-pressure p-V data were fitted to the Parsafar-Mason equation of state with an accuracy better than 1%.