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Multiscale quantum/atomistic coupling using constrained density functional theory

机译：基于约束密度泛函理论的多尺度量子/原子耦合

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摘要

Multiscale coupling of a quantum mechanical (QM) domain to a coarser-scale material description in a larger surrounding domain should yield forces and energies in the QM domain that are the same as would be achieved in a QM simulation of the entire system. Here, such a coupling is achieved by using constrained density functional theory (DFT) in which the quantum mechanical interaction between the domains is captured via a constraint potential arising from an imposed constraint on the charge density in a boundary region between the two domains. The implementation of the method, including the construction of the constraint charge density and the calculation of the constraint potential, is presented. The method is applied to problems in three different metals (Al, Fe, and Pd) and is validated against periodic DFT calculations. The method reproduces the QM charge density and magnetic moments of bulk materials, produces a reasonable edge dislocation core structure for Fe, and also gives accurate vacancy formation energy for Al and chemisorption energy on a flat Pd surface. Finally, the method is used to study the chemisorption energy of CO on a stepped Pd surface. In general, the method can mitigate fictitious interactions between surface steps and other extended defects, and accommodate long-range deformation fields, and thus improves upon periodic DFT calculations.
机译：量子力学（QM）域与较大范围内的较粗略材料描述的多尺度耦合应在QM域中产生与整个系统的QM模拟中相同的力和能量。在此，通过使用约束密度泛函理论（DFT）来实现这种耦合，其中，通过对两个畴之间的边界区域中的电荷密度施加约束而产生的约束电位来捕获畴之间的量子力学相互作用。提出了该方法的实现方法，包括约束电荷密度的构建和约束电位的计算。该方法适用于三种不同金属（Al，Fe和Pd）中的问题，并针对定期DFT计算进行了验证。该方法再现了块状材料的QM电荷密度和磁矩，为Fe生成了合理的边缘位错核心结构，还为Al提供了准确的空位形成能和在平坦的Pd表面上的化学吸附能。最后，该方法用于研究阶梯状Pd表面上CO的化学吸附能。通常，该方法可以减轻表面台阶与其他扩展缺陷之间的虚拟相互作用，并适应远距离变形场，因此可以改进定期DFT计算。

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