The latest version of MRCC is released on March 18, 2022.

A detailed review of the MRCC capabilities up to the 2020 version is available in J. Chem. Phys. 152, 074107 (2020). https://doi.org/10.1063/1.5142048 
Users of the current and all previous MRCC versions are kindly requested to use the corresponding citation format in any publication utilizing MRCC.

The important new features and changes are as follows.

1) Explicitly correlated MP2, CCSD, and CCSD(T) programs. A new explicitly correlated triple excitation correction, termed (T+). https://doi.org/10.1063/5.0057426

2) Highly competitive restricted open-shell local MP2 program and corresponding double hybrid functionals. https://doi.org/10.1021%2Facs.jctc.1c00093

3) New, very efficient, and parallel reduced-cost density fitting CCSD(T) program utilizing the frozen natural orbital and the natural auxiliary function approximations. https://doi.org/10.1021%2Facs.jctc.0c01077

4) Improved basis set truncation corrections for frozen natural orbital CCSD(T) energies. https://doi.org/10.1080/00268976.2021.1963495

5) Range-separated double hybrid functionals, where both the exchange and the correlation terms are separated. New range-separated double hybrids for excited states. https://doi.org/10.1021%2Facs.jctc.0c01135

6) Spin-component-scaled range-separated double hybrids for excited states. https://doi.org/10.1021/acs.jctc.1c00422

7) ADC(2)-based range-separated double hybrids for excited states. https://doi.org/10.1021/acs.jctc.1c01100  https://doi.org/10.1021/acs.jctc.1c01307

8) Multipole-accelerated calculation of the exchange contribution in density fitting Hartree-Fock and Kohn-Sham algorithms. https://doi.org/10.1080/00268976.2020.1769213

9) New reduced-cost Hartree-Fock and Kohn-Sham algorithms: occ-RI, dual auxiliary basis, dual metric DF-SCF, and dual grid COSX. https://doi.org/10.1063%2F5.0041276

10) Interface to the xTB and Mopac semi-empirical programs. ONIOM calculations with semi-empirical layers. Charge-correction schemes for the electronic embedding.

11) Implementation of the embedded cluster reference interaction site model (EC-RISM) with atomic charges for the computation of solvation thermodynamics. Determination of atomic charges based on the electrostatic potential.

12) Implementation of the core-valence separation for arbitrary (linear-response) coupled-cluster methods.

13) An efficient and parallel density fitting MP3 implementation and corresponding third-order double hybrid functionals.

14) Additional control over the SCF acceleration techniques and an improved SCF initial guess using semi-empirical methods. https://doi.org/10.1002/qua.26782

15) Generalized Boys localization of Jansik et al. using the m-th power of orbital variance.

16) A couple of bugs have been fixed, and the manual has been improved.

It is recommended for every user to upgrade to this version.