**ABSTRACT**

Recent astrophysical observations show that the universe has entered a late-time accelerated expansion period. It is commonly accepted that the dark energy is responsible for this enigmatic behavior of our universe, because it makes up about 70 percent of the content of our universe and dominates over the matter part. Therefore, the dark energy will govern the speedy enlargement and determine the fate of our universe. Another interpretation of the dark energy is that this is a new kind of dynamical field or fluid, something mysterious which fills all of space but something whose influence on the accelerated enlargement nature of our universe is the opposite of that of baryonic matter and ordinary energy. Here, we focus on the polytropic gas unified dark matter-energy model in a 5-dimensional cosmology to reconstruct tachyonic scalar field proposal of the dark energy. It is known that the background dynamics of the polytropic gas is equivalent to that one for the dark energy interacting with the dark matter. On the other hand, using scalar field is one of the most significant methods helping us to understand the dark universe. There are many scalar field proposals, but generally it is hard to get exact relations for the scalar field function and its self-interacting potential. In this work, making use of the 5-dimensional Polytropic gas model, we calculate exact relations for the tachyonic scalar field. After that, we discuss our theoretical calculations graphically in order to interpret our theoretical results in a different way.

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