supplement information (SI)

The supplementary material contains the results of band structure of Mg2C and Mg2Si, and the optical spectra (ε_2,ε_1,n,k and R) of Mg2C without considering local field effects. The tabulated comparison of energy peak positions of ε_2, k and R with LFE calculated using RPA, LRC and BS kernels are presented. The peak positions of EEL spectra computed using RPA and three XC kernels, with and without incorporating LFE are also included in the supplementary material.

本补充材料包含了Mg₂C与Mg₂Si的能带结构计算结果，以及未考虑局域场效应（local field effects, LFE）的Mg₂C光学光谱数据，具体涵盖介电函数虚部ε₂、介电函数实部ε₁、折射率n、消光系数k与反射率R。本补充材料还提供了采用随机相位近似（Random Phase Approximation, RPA）、长程修正（Long-Range Correction, LRC）以及贝特-萨尔皮特核（Bethe-Salpeter kernels, BS kernels）计算得到的、考虑局域场效应（LFE）的ε₂、k与R的能量峰位制表对比结果。此外，本补充材料还收录了采用RPA与三种交换关联泛函核（exchange-correlation kernels, XC kernels）计算得到的电子能量损失谱（Electron Energy Loss Spectroscopy, EEL spectra）的峰位数据，涵盖考虑与未考虑局域场效应（LFE）两种情形。