To capture the underlying chemistry and physics of a system on electronic structure platform, it is necessary to accurately describe the intermolecular interactions such as repulsion, polarization, hydrogen bonding, and van der Waals interactions. Among these interactions, van der Waals (dispersion) interactions are weak in nature as compare to covalent bonds and hydrogen bonding, but it is physically and chemically very important in accurately predicting condensed phase properties such as Vapor liquid equilibria. This presents a significant challenge in modeling VLE using a first principles approach. However, recent developments in dispersion corrected (DFT-D3) and nonlocal density functionals can model dispersion interactions with reasonable accuracy. Here, we will present some of results that quantify efficacy of recent density functionals in predicting phase equilibria of molecular systems via first principle Monte Carlo (FPMC) simulations. Our aim is to assess the performance of several density functional by determining VLE, critical properties, dimer potential energy curves, vibrational spectra, and structural properties. The functional used in our study includes PBE-D3, BLYP-D3, rVV10, PBE0- D3, and M062X-D3. In addition, we have used the second order Møller-Plesset perturbation theory (MP2) method for computing density of argon at single temperature. The organic compounds considered for this study involves argon, CO2, SO2, and various hydroflurocarbons (R14, R134a, CF3H, CF2H2, CFH3) molecules. Additionally, the development of new materials, ionic liquids, and modification of industrial processes are an ongoing effort by researchers to efficiently capture acidic gases. Our ability to model these sorption processes using a first principles approach can have significant impact in speeding up the discovery process. In our work, we have predicted CO2 solubility in triethyl(butyl)phosphonium ionic liquid via FPMC simulations. Our results reveal the infrared spectra, structural and transport properties for pure ionic liquid and its mixture with CO2 through ab initio molecular dynamics simulations.