The local pair-natural orbital (DLPNO) based coupled cluster method have been managed to investigate large organic molecule and small proteins (linear C150H302 (452 atoms, >8800 basis functions) , Crambin with 644 atoms, and more than 6400 basis functions ,C350H902 (>1000 atoms, > 20000 basis functions)).
Riplinger, C., Sandhoefer, B., Hansen, A., & Neese, F. (2013). Natural triple excitations in local coupled cluster calculations with pair natural orbitals. The Journal of chemical physics, 139(13), 134101.
Riplinger, C., Pinski, P., Becker, U., Valeev, E. F., & Neese, F. (2016). Sparse maps—A systematic infrastructure for reduced-scaling electronic structure methods. II. Linear scaling domain based pair natural orbital coupled cluster theory. The Journal of chemical physics, 144(2), 024109.
In recent years, considerable amount of effort has been made on developing linear scaling coupled cluster methods. These methods have been implemented in the electronic structure package ORCA which is developed by Max Planck Institute, Germany.