The effect of molecular structure and environment on electron transport in nanoscale systems is a crucial aspect of understanding and designing efficient nanoscale electronic devices. The transport properties of a molecular system are influenced by factors such as the molecular structure, the nature of the chemical bonds, the presence of functional groups, and the surrounding environment e.g., solvents, temperature, and pressure . In this analysis, we will focus on a specific molecular system, the single-molecule junction, and use quantum mechanical methods and computational simulations to study its electron transport properties.A single-molecule junction consists of a single molecule connected to two metallic electrodes. One of the most studied single-molecule junctions is the benzene-1,4-dithiol BDT molecule, which consists of a benzene ring with two thiol -SH groups at the 1 and 4 positions. This molecule can form a junction by binding its thiol groups to gold electrodes.To analyze the electron transport properties of the BDT single-molecule junction, we can employ quantum mechanical methods such as density functional theory DFT and non-equilibrium Green's function NEGF formalism. DFT allows us to calculate the electronic structure of the molecule, while NEGF enables us to compute the electron transport properties, such as the transmission coefficient and the current-voltage I-V characteristics.Using DFT, we can optimize the geometry of the BDT molecule and calculate its electronic structure, including the highest occupied molecular orbital HOMO and the lowest unoccupied molecular orbital LUMO . The energy difference between the HOMO and LUMO, known as the HOMO-LUMO gap, is an essential parameter that determines the electron transport properties of the molecular junction.Next, we can use the NEGF formalism to compute the transmission coefficient as a function of energy. The transmission coefficient quantifies the probability of an electron to be transmitted through the molecular junction. The calculated transmission coefficient can be used to compute the electrical conductance and the I-V characteristics of the BDT single-molecule junction.The effect of the environment on the electron transport properties of the BDT single-molecule junction can be studied by considering different solvents or varying the temperature and pressure in the computational simulations. For example, the presence of a polar solvent can lead to the formation of solvent-induced dipoles, which can affect the alignment of the molecular orbitals and, consequently, the electron transport properties.In conclusion, the electron transport properties of nanoscale systems, such as the BDT single-molecule junction, are strongly influenced by the molecular structure and the surrounding environment. Quantum mechanical methods, such as DFT and NEGF, combined with computational simulations, provide valuable insights into the underlying mechanisms and can help guide the design of efficient nanoscale electronic devices.