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arXiv 1409.7285cond-mat.mtrl-sci
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有机分子在TiO2(110)表面的吸附:范德华相互作用的影响

Adsorption of organic molecules at the TiO2(110) surface: the effect of van der Waals interactions

Marcus Tillotson, Peter Brett, Roger A. Bennett, Ricardo Grau-Crespo

摘要:

了解有机分子与TiO 2表面的相互作用对于广泛的技术应用非常重要。虽然密度泛函理论(DFT)计算可以提供有关这些相互作用的有价值的见解,传统的DFT方法与本地交换相关泛函遭受非键范德华(vdW)相互作用的描述差。我们在这里研究的贡献vdW力的小有机分子(甲烷,甲醇,甲酸和甘氨酸)与TiO 2(110)表面的相互作用,基于DFT计算与optB 88-vdW功能。在标准广义梯度近似(GGA-PBE)下得到了不同构型的吸附几何构型和吸附能。我们发现,optB 88-vdW始终提供较短的表面吸附物到表面的距离和略强的相互作用比PBE弱(物理吸附)的吸附模式。在强烈吸附(化学吸附)的分子的情况下,这两个泛函给出类似的结果的吸附几何形状,也类似的值的相对能量之间的不同的化学吸附模式为每个分子。特别是这两个功能预测,解离吸附比分子吸附甲醇,甲酸和甘氨酸更有利,在一般协议与实验。从这两个泛函得到的离解能也非常相似,表明VDW相互作用不影响表面去质子化的热力学。然而,optB 88-vdW总是预测比PBE更强的吸附。甲醇吸附能与从Redhead程序升温脱附数据分析获得的值的比较表明,optB 88-vdW显着高估的吸附强度,虽然我们警告这种比较中涉及的不确定性。

英文摘要:

Understanding the interaction of organic molecules with TiO2 surfaces is important for a wide range of technological applications. While density functional theory (DFT) calculations can provide valuable insight about these interactions, traditional DFT approaches with local exchange-correlation functionals suffer from a poor description of non-bonding van der Waals (vdW) interactions. We examine here the contribution of vdW forces to the interaction of small organic molecules (methane, methanol, formic acid and glycine) with the TiO2 (110) surface, based on DFT calculations with the optB88-vdW functional. The adsorption geometries and energies at different configurations were also obtained in the standard generalized gradient approximation (GGA-PBE) for comparison. We find that the optB88-vdW consistently gives shorter surface adsorbate-to-surface distances and slightly stronger interactions than PBE for the weak (physisorbed) modes of adsorption. In the case of strongly adsorbed (chemisorbed) molecules both functionals give similar results for the adsorption geometries, and also similar values of the relative energies between different chemisorption modes for each molecule. In particular both functionals predict that dissociative adsorption is more favourable than molecular adsorption for methanol, formic acid and glycine, in general agreement with experiment. The dissociation energies obtained from both functionals are also very similar, indicating that vdW interactions do not affect the thermodynamics of surface deprotonation. However, the optB88-vdW always predicts stronger adsorption than PBE. The comparison of the methanol adsorption energies with values obtained from a Redhead analysis of temperature programmed desorption data suggests that optB88-vdW significantly overestimates the adsorption strength, although we warn about the uncertainties involved in such comparisons.

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