  Stellar chemical abundances are crucial and fundamental in astrophysics.
However, they could suffer from substantial systematic errors according to
several investigations but still lack calibrations in bulk. By using Gaia wide
binaries, we find the temperature-dependent bias between the two binary
components for [Fe/H] and [alpha/Fe] measurements from the LAMOST
low-resolution spectra and Gaia RVS spectra. At Teff=4000 K, the LAMOST [Fe/H]
is significantly underestimated by approximately 0.4 dex, compared with its
typical uncertainty of 0.1 dex. Its [alpha/Fe] is overestimated by about 0.2
dex. For Gaia, the underestimation of [M/H] and overestimation of [alpha/Fe]
becomes pronounced near 7000 K with smaller magnitudes. We perform an internal
calibration by minimizing the differences between binary components and provide
the correction curves. After corrections, the standard deviations of the
residuals compared to the PASTEL catalog decrease from about 0.045/0.1 to
0.02/0.043 for LAMOST and Gaia, respectively. The chemical homogeneity of the
open cluster M 44 is also improved by a factor of two. We stress that the
underestimation of [Fe/H] could lead to an overestimation of binary fractions
when selecting binary stars by the excess of luminosity. The method of this
work could be applied to other data-sets in the future. Our results will
benefit statistic studies that use LAMOST and Gaia samples with a wide
temperature range.
