In this work, we propose a new auxetic (negative Poissons ratio values) structure, based on a $gamma$-graphyne structure, here named $Agamma G$ $structure$. Graphynes are 2D carbon allotropes with phenylic rings connected by acetylenic groups. The A$gamma$G structural/mechanical and electronic properties, as well as its thermal stability, were investigated using classical reactive and quantum molecular dynamics simulations. We found that A$gamma$G has a large bandgap of 2.48 eV and is thermally stable at a large range of temperatures. It presents a Youngs modulus that is an order of magnitude smaller than that of graphene or $gamma$-graphyne. The classical and quantum results are consistent and validate that the A$gamma$G is auxetic, both when isolated (vacuum) and when deposited on a copper substrate. We believe that this is the densest auxetic structure belonging to the graphyne-like families.
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