The magnetic circular X-ray dichroism (XMCD) in X-ray absorption spectroscopy (XAS) is extensively used to monitor the response of a magnetic system to an external perturbation. Application of a static external electric field to control its magnetic properties may just lead to a charge rearrangement or to a steady electric current dependent on the geometry. As it is demonstrated, the first situation can be handled with minor modifications of the standard well established schemes to calculate XAS and XMCD spectra. For the second case, however, more advanced schemes have to be used that account for the steady-state out-of-equilibrium situation. It is shown, that this can indeed be achieved by making use of the Keldysh non-equilibrium Green function formalism that allows in particular to express the X-ray absorption coefficient in terms of the corresponding greater Green function $G^{>}\left(E\right)$. As an alternative approach, a bi-linear response formalism is presented that can be used to calculate the modification of the XMCD spectra due to the electric field directly.

X 射线吸收光谱 (XAS) 中的磁圆 X 射线二色性 (XMCD) 广泛用于监测磁系统对外部扰动的响应。应用静态外部电场来控制其磁性可能只会导致电荷重排或稳定电流取决于几何形状。正如所证明的，第一种情况可以通过对计算 XAS 和 XMCD 光谱的标准完善方案进行少量修改来处理。然而，对于第二种情况，必须使用更先进的方案来解决稳态非平衡情况。结果表明，这确实可以通过利用凯尔迪什非平衡格林函数形式来实现，该形式特别允许用相应的更大格林函数来表达 X 射线吸收系数$G^{>}（乙）$。作为一种替代方法，提出了一种双线性响应形式，可用于直接计算由电场引起的 XMCD 光谱的修改。