Spin adapted restricted open shell coupled cluster theory. Linear version

We describe the linear version of the spin adapted coupled cluster theory with all single and double excitations for open shell systems in restricted Hartree–Fock formalism. The method is based on the partitioning of the Hamiltonian developed by Hubač and Čársky [I. Hubač and P. Čársky, Phys. Rev. A 22, 2392 (1980)] in restricted Roothaan open shell formalism. Correlation energy of some simple molecular systems is calculated.