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首页> 外文期刊>Acta biomaterialia >Mechanical properties, electronic structure and bonding of alpha- and beta-tricalcium phosphates with surface characterization.
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Mechanical properties, electronic structure and bonding of alpha- and beta-tricalcium phosphates with surface characterization.

机译：机械性能，电子结构以及α-和β-三钙磷酸酯的表面特征键合。

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The mechanical properties and electronic structure of alpha- and beta-tricalcium phosphate (TCP) crystals are studied by using two ab initio density functional methods, the Vienna Ab initio Simulation Package (VASP) and the orthogonalized linear combination of atomic orbitals method. Based on the VASP optimized crystal structures, the elastic constants of alpha- and beta-TCP are obtained using an effective stress-strain computational scheme. From the calculated elastic constants, the bulk modulus, shear modulus, Young's modulus and Poisson's ratios are obtained. The results show that the mechanical properties of the two crystals are comparable and that alpha-TCP is somewhat softer than beta-TCP. Comparison with experimental extrapolations of the elastic constants shows significant differences, which attest to the difficulty of obtaining single crystal samples. The calculated electronic structure results show that both crystals are large gap insulators with a direct band gap of 4.89 eV for alpha-TCP and 5.25 eV for beta-TCP. Effective charge calculations show that, on average, beta-TCP has slightly less charge transfer per Ca than alpha-TCP. The (010) ((001)) surface model for alpha-TCP (beta-TCP) is studied using a supercell slab geometry and fully relaxed to obtain the optimized structures. The estimated surface formation energies are 0.777 and 0.842 J m(-2) for alpha-TCP and beta-TCP, respectively. The electronic structures of the two surface models are compared with the bulk models. Charge density analysis shows that the surfaces of both TCP crystals are positively charged overall owing to the presence of Ca ions near the surfaces.
机译：通过使用两种从头算密度函数方法，维也纳从头算模拟程序包（VASP）和原子轨道正交线性组合方法研究了α-和β-三钙磷酸（TCP）晶体的机械性能和电子结构。基于VASP优化的晶体结构，使用有效的应力-应变计算方案可获得α-和β-TCP的弹性常数。根据计算出的弹性常数，可得到体积模量，剪切模量，杨氏模量和泊松比。结果表明，两种晶体的机械性能相当，并且α-TCP比β-TCP稍软。与弹性常数的实验外推比较表明存在明显差异，这证明了获得单晶样品的困难。计算得到的电子结构结果表明，两种晶体都是大间隙绝缘体，α-TCP的直接带隙为4.89 eV，β-TCP的直接带隙为5.25 eV。有效的电荷计算表明，平均而言，β-TCP的每Ca电荷转移量比α-TCP少。使用超级单元平板几何图形研究了alpha-TCP（beta-TCP）的（010）（（001））表面模型，并完全放松以获得优化的结构。对于α-TCP和β-TCP，估计的表面形成能分别为0.777和0.842 J m（-2）。将两个表面模型的电子结构与整体模型进行比较。电荷密度分析表明，由于在表面附近存在Ca离子，两个TCP晶体的表面总体上带正电。

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