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What Rules the Relative Stability of α-, β-, and γ-Glycine Polymorphs?
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2020-05-13 , DOI: 10.1021/acs.cgd.0c00489 Neubi Francisco Xavier 1 , Antônio Marques da Silva 1 , Glauco F. Bauerfeldt 1
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2020-05-13 , DOI: 10.1021/acs.cgd.0c00489 Neubi Francisco Xavier 1 , Antônio Marques da Silva 1 , Glauco F. Bauerfeldt 1
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Theoretical calculations based on the density functional theory, using the PBE functional with the D3 dispersion correction under periodic boundary conditions, have been employed aiming to investigate the properties of α-, β-, and γ-glycine. Structural parameters have been predicted with a maximum error of 1.42% for lattice parameters and 2.53% for the unit-cell volume, for the α phase. Band structure calculations suggest the band gap values of 4.80, 5.01, and 5.23 eV for the α, β, and γ phases, respectively. Quasi-harmonic calculations have been performed and the Gibbs free energy function has been calculated in a wide range of temperature and pressures, suggesting the stability ordering γ > α > β, at room temperature, and the γ to α-glycine phase transition temperature of 442.55 K, at 1 bar, in agreement with the experimental findings. Moreover, a deviation from the experimental value of only 0.44 J mol–1 K–1 is observed for the predicted S(α→γ) at 298.15 K. Finally, calculated sublimation enthalpies of 140.58, 138.09, and 141.70 kJ mol–1 (α, β, and γ-glycine, respectively), at 298.15 K and 1 bar, have also shown good agreement with the experimental values.
中文翻译：
什么规则决定了α-，β-和γ-甘氨酸多晶型的相对稳定性？
为了研究α-，β-和γ-甘氨酸的性质，已采用基于密度泛函理论的理论计算，该算法使用具有周期性边界条件下的D3色散校正的PBE泛函。预测结构参数，对于α相，晶格参数的最大误差为1.42％，晶胞体积的最大误差为2.53％。带结构计算表明，α，β和γ相的带隙分别为4.80、5.01和5.23 eV。已经进行了准谐波计算，并在很宽的温度和压力范围内计算了吉布斯自由能函数，这表明在室温下，γ>α>β的稳定性顺序为：γ>α>甘氨酸的相变温度。在1 bar下达到442.55 K，与实验结果一致。在298.15 K处观察到–1 K –1的预测的S （α→γ）。最后，计算出的升华焓为140.58、138.09和141.70 kJ mol –1（分别为α，β和γ-甘氨酸）。 298.15 K和1 bar也显示出与实验值的良好一致性。
更新日期：2020-07-01
中文翻译：
什么规则决定了α-，β-和γ-甘氨酸多晶型的相对稳定性？
为了研究α-，β-和γ-甘氨酸的性质，已采用基于密度泛函理论的理论计算，该算法使用具有周期性边界条件下的D3色散校正的PBE泛函。预测结构参数，对于α相，晶格参数的最大误差为1.42％，晶胞体积的最大误差为2.53％。带结构计算表明，α，β和γ相的带隙分别为4.80、5.01和5.23 eV。已经进行了准谐波计算，并在很宽的温度和压力范围内计算了吉布斯自由能函数，这表明在室温下，γ>α>β的稳定性顺序为：γ>α>甘氨酸的相变温度。在1 bar下达到442.55 K，与实验结果一致。在298.15 K处观察到–1 K –1的预测的S （α→γ）。最后，计算出的升华焓为140.58、138.09和141.70 kJ mol –1（分别为α，β和γ-甘氨酸）。 298.15 K和1 bar也显示出与实验值的良好一致性。
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