Hund's physics and the magnetic ground state of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>CrO</mml:mi><mml:mi>X</mml:mi></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mrow><mml:mi>X</mml:mi><mml:mo>=</mml:mo><mml:mtext>Cl</mml:mtext><mml:mo>,</mml:mo><mml:mspace width="0.16em" /><mml:mtext>Br</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:math>

To understand the magnetic property of layered van der Waals materials CrOX (X = Cl, Br), we performed detailed first-principles calculations for both bulk and monolayer. We found that charge-only density functional theory combined with explicit on-site interaction terms (so-called cDFT$+U$) well reproduces experimental ground state CrOX, which is not case use spin-dependent sDFT$+U$). Unlike some previous studies, our results show monolayers are antiferromagnetic as in bulk. It also consistent force linear response calculation exchange couplings $J_{\rm ex}$. The result orbital-decomposed ex}$ shows Cr $t_\textrm{2g}$-$t_\textrm{2g}$ component mainly contributes to order Our analysis taking correct Hund's physics into account key importance construct phase diagram describe electronic structure.