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The electronic spectral function of BaNi$_2$As$_2$ is investigated using boththe angle-resolved photoemission spectroscopy (ARPES) and a combinedcomputational scheme of local density approximation together with dynamicalmean-field theory (LDA+DMFT). In contrast to well studied isostructural ironarsenide high temperature superconductors, the BaNi$_2$As$_2$ demonstrate weakcorrelation effects although Ni-3d elections have even lager on-siteinteraction than Fe-3d ones. LDA+DMFT effective mass enhancement for bandscrossing the Fermi level is found to be only about $1.2$ which agrees well withARPES data. This reduction of the correlation manifestation with respect toiron pnictides comes from the increase of 3d-orbital filling, when going fromFe to Ni. The electron correlations cause remarkable reconstruction of the bareBaNi$_2$As$_2$ LDA band structure below $-0.8$ eV due to self-energy effect. Asimplified toy model to understand weakness of correlation effects inBaNi$_2$As$_2$ and to describe the LDA+DMFT self-energy shape is discussed. Formore realistic comparison of LDA+DMFT spectral function maps with ARPES data wetake into account several experimental features: the photoemissioncross-section, the experimental energy and angular resolutions and thephoto-hole lifetime effects. Thus presented here LDA+DMFT calculations withexperimental features included provide nearly qualitative agreement with ARPESdata and assure the observation of a dramatic apparent decrease of thecorrelation strength compared to the Fe compounds.

Weakness of Correlation Effect Manifestation in BaNi$_2$As$_2$: ARPES and LDA+DMFT study