This psi4 plugin is intended to test the performance of the frozen virtual natural orbitals based methods in calculating coupled cluster response properties. This plugin is built on the the latest persion of psi41.1 which can be found at https://github.com/psi4/psi4. The full set of instructions for downloading and installing psi4 can be found at http://psicode.org/psi4manual/master/build_faq.html#obtaining-and-updating-psifour. After installing psi4, one can create plugins by following the instructions provided in the psi4 manual, http://www.psicode.org/psi4manual/master/plugins.html. Since all the necessay files have alredy been added in this repo, one needs to follow these three steps to compile and run this plugin in your top directory. 1. `psi4 --compile-plugin` 2. make 3. psi4 .