Scientists and researchers often need to run midscale to large-scale scientific computations on powerful computing machines or platforms. Even with today's available powerful computing platforms, many of these computations still take enormous runtime. With the advent of cloud computing technology, scientists are now able to reduce significantly the computational time by outsourcing computation functions to the cloud systems. We show in this paper how AWS (Amazon Web Services) cloud computing platform can be automated in executing large-scale computationally expensive scientific experiments. Specifically, we show how quantum chemistry simulations can be executed in parallel and in a cluster-based fashion using the publicly available and popular Amazon cloud platform. With Amazon cloud, we were able to reduce the computation time by almost five orders of magnitude. In addition, the paper offers many important useful guidelines, scripts, and commands for scientists and researchers on how to automate and execute parallel and cluster-based scientific jobs on any cloud platform.