<p>Copper is extensively used in industrial components operating under high pressure and extreme mechanical environments, making it essential to understand its structural response under such conditions. In this study, molecular dynamics (MD) simulations are conducted to investigate the phase transition in single-crystal copper at room temperature (300 K) under uniaxial compression. The simulations reveal that as strain (ε) increases, copper undergoes a structural transformation, with more than 90% of FCC atoms converting to the BCC phase at a strain of 0.24, corresponding to a stress (σ) of approximately 64 GPa. Nearly complete (&gt; 99%) phase transition from FCC to BCC is observed which is a unique observation likely being reported for the first time. Although metastable, the BCC structure remains over an appreciable strain range, which may lead to a complete change in the failure mechanics of copper under extreme constrained compression, as the mechanical behavior of BCC and FCC lattice structures differs. This phase transformation is accompanied by a progressive rearrangement of atomic structures, driven by increasing stress and geometric constraints.</p> Graphical Abstract <p></p>