Surface reconstructions in thin films of magnetic topological insulator <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">MnBi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">T

Understanding the nature of surface states and their exchange gaps in magnetic topological insulator <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>MnBi</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>Te</a:mi><a:mn>4</a:mn></a:msub></a:mrow></a:math> (MBT) thin films is crucial for achieving robust topological Chern and axion insulating phases where the quantum anomalous Hall effect and topological magneto-electric effect can be realized. Here we focus on some rather unexplored features of possible surface reconstructions of interstitial-2H and peripheral-2H types, which are likely to occur in experiments. Using first-principles calculations together with molecular dynamics simulations accelerated by a machine learning force field, we demonstrate that interstitial-2H and peripheral-2H type atomic reconstructions play a crucial role in modifying the exchange gap and surface characteristics of MBT thin films, alongside previously reported factors such as surface magnetism, stacking configurations, and native defects. Moreover, these surface reconstructions have important implications for the topological indices and the nature of quasi-one-dimensional side-wall edge states dominating quantum transport. Specifically, the calculation of the energy landscape and barriers for the proposed surface reconstructions indicates that the interstitial-2H reconstruction is thermodynamically more stable than the peripheral-2H reconstruction. The latter case is also hypothesized as providing a plausible explanation for the Rashba surface states observed in angle-resolved photoemission spectroscopy measurements. Our analysis provides a theoretical framework to elucidate the nature and effect of reconstructions in <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msub><b:mi>MnBi</b:mi><b:mn>2</b:mn></b:msub><b:msub><b:mi>Te</b:mi><b:mn>4</b:mn></b:msub></b:mrow></b:math> thin films, with predictions for the experimental realization of different topological phases.