However, a more pronounced deviation is observed for optical modes, indicating a higher error in reproducing their frequencies. This observed discrepancy may arise from the inherently challenging nature of capturing intricate details associated with higher-energy optical vibrations. To assess the magnitude of errors in comparison with experimental data, we specifically consider cubic diamond's longitudinal optical (LO) modes for which reliable ex-collected by Hoffman et al., we confirmed that one of the structures is a new C polymoprh.