The exact form of the kinetic energy functional has remained elusive in orbital-free models of density functional theory (DFT). This has been the main stumbling block for the development of a general-purpose framework on this basis. Here, we show that on the basis of a two-density model, which represents many-electron systems by mass density and spin density components, we can derive the exact form of such a functional. The exact functional is shown to contain previously suggested functionals to some extent, with the notable exception of the Thomas-Fermi kinetic energy functional.

中文翻译：

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精确的无轨道动能，适用于一般的多电子系统

动能泛函的确切形式在密度泛函理论（DFT）的无轨道模型中仍然难以捉摸。在此基础上，这一直是开发通用框架的主要绊脚石。在这里，我们表明，在一个通过密度和自旋密度分量表示多电子系统的双密度模型的基础上，我们可以得出这种函数的精确形式。确切的功能显示出在一定程度上包含先前建议的功能，但托马斯-费米动能功能是一个明显的例外。