A fundamental belief is that the formulism of relativistic quantum mechanics equations (RQMEs) should remain in low momentum motion. However, it is found that some formulas from RQMEs were lost in Schrdinger equation. For example, a free relativistic particle has positive and negative energy branches. The former includes positive kinetic energy (PKE) and the latter negative kinetic energy (NKE). The latter should be treated on an equal footing as the former. Nevertheless, from Schrdinger equation, a free particle can have only PKE. Starting from RQMEs and taking low momentum approximation, we derive NKE Schrdinger equation which is for the cases that free particles have NKE. Thus negative energy branch of RQMEs can be retained in low momentum motion. We point out a fact that whether Schrdinger equation is applicable in a region where a particle’s energy E is less than potential V, E<V, has never been quantitatively verified. In such a region NKE Schrdinger equation should be employed. With the help of NKE Schrdinger equation, the lost formulas are recovered. The so-called difficulty of negative probability of Klein–Gordon equation for free particles is solved. A PKE (NKE) particle can have stationary motion only when it is subject to an attractive (repulsive) potential, which is determined by Virial theorem. Two NKE electrons in a potential can constitute a stable system, a new kind of possible mechanism for electron paring. The whole discussion stems from RQMEs with no any new postulation. Experiments are suggested, which may confirm that there are indeed NKE electrons.

一个基本的信念是，相对论量子力学方程（RQME）的公式应该保持在低动量运动中。但是，发现在Schrdinger方程中丢失了一些来自RQME的公式。例如，自由相对论粒子具有正和负能量分支。前者包括正动能（PKE），后者包括负动能（NKE）。后者应与前者同等对待。但是，根据薛定inger方程，自由粒子只能具有PKE。从RQME开始，并采用低动量近似，我们推导了NKE Schrdinger方程，该方程适用于自由粒子具有NKE的情况。因此，RQME的负能量分支可以保持在低动量运动中。E小于电位V，E < V，尚未经过定量验证。在这种区域，应采用NKE Schrdinger方程。借助NKE Schrdinger方程，可以恢复丢失的公式。解决了自由粒子的Klein-Gordon方程的负概率的难度。仅当PKE（NKE）粒子具有吸引力（排斥力）时，它才能具有平稳运动，这由维里尔定理确定。电位中的两个NKE电子可以构成一个稳定的系统，这是一种新型的电子削皮机制。整个讨论源于RQME，没有任何新的假设。建议进行实验，可以确认确实存在NKE电子。