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arXiv 1406.7609physics.chem-phphysics.comp-ph
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轨道占据分数的Kohn-Sham理论中的强关联和电荷局域化

Strong correlation and charge localisation in Kohn-Sham theories with fractional orbital occupations

Maria Hellgren, Tim Gould

摘要:

我们研究了静态相关和离域误差,并表明即使是具有良好能量的方法也会产生影响密度的显著离域误差,从而导致预测{ \em例如}的大误差。偶极矩我们说明了这一点,通过比较现有的最先进的方法与一个准确的交换相关功能的基础上广义的价键的anananterior,其中轨道和分数职业被视为变分参数通过优化的有效势(OEP)。我们发现,OEP具有台阶和峰值的功能,类似于精确的Kohn-Sham(KS)的DFT潜力,是至关重要的,以防止电荷离域。我们进一步表明,这一步是失踪的减少密度矩阵泛函理论中常见的近似导致离域误差相比,在DFT近似。最后,我们解释了离域误差来自一个人工混合的基态与电荷转移激发态,这是避免,如果占领数表现出不连续性。

英文摘要:

We study static correlation and delocalisation errors and show that even methods with good energies can yield significant delocalization errors that affect the density, leading to large errors in predicting {\em e.g.} dipole moments. We illustrate this point by comparing existing state-of-art approaches with an accurate exchange correlation functional based on a generalised valence-bond ansatz, in which orbitals and fractional occupations are treated as variational parameters via an optimized effective potential (OEP). We show that the OEP exhibits step and peak features which, similar to the exact Kohn-Sham (KS) potential of DFT, are crucial to prevent charge delocalization. We further show that the step is missing in common approximations within reduced density matrix functional theory resulting in delocalization errors comparable to those found in DFT approximations. Finally, we explain the delocalization error as coming from an artificial mixing of the ground state with a charge-transfer excited state which is avoided if occupation numbers exhibit discontinuities.

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