In a few years, we will have in Europe the first generation of exascale machines. To harness this huge computational power, new software strategies need to be devised and this requires a significant, joint effort of domain scientists and computational experts. To this aim, the European Commission funds targeted Centers of Excellence, each to empower a specific scientific community. TREX has been awarded Center of Excellence for the community of quantum chemistry. TREX federates European scientists, High Performance Computing stakeholders, and SMEs to develop and apply high-performance software solutions for quantum mechanical simulations at the exascale.