  The eT program is an open source electronic structure package with emphasis
on coupled cluster and multilevel methods. It includes efficient spin adapted
implementations of ground and excited singlet states, as well as equation of
motion oscillator strengths, for CCS, CC2, CCSD, and CC3. Furthermore, eT
provides unique capabilities such as multilevel Hartree-Fock and multilevel
CC2, real-time propagation for CCS and CCSD, and efficient CC3 oscillator
strengths. With a coupled cluster code based on an efficient Cholesky
decomposition algorithm for the electronic repulsion integrals, eT has similar
advantages as codes using density fitting, but with strict error control. Here
we present the main features of the program and demonstrate its performance
through example calculations. Because of its availability, performance, and
unique capabilities, we expect eT to become a valuable resource to the
electronic structure community.
