Functionalities of MPGRAD, RIMP2, and RICC2

TURBOMOLE offers three possibilities for the calculation of MP2 data. A "conventional" implementation [84], mpgrad, based on the calculation of four-center integrals (not further developed for several years), and two treatments within the resolution-of-the-identity (RI) approximation: the first and stand-alone implementation [8], rimp2, and within the coupled-cluster program [10], ricc2.

Functionality of mpgrad:

• Calculation of MP2 energies and/or MP2 gradients for RHF and UHF wave functions.
• The frozen core approximation (possibility to exclude low-lying orbitals from the MP2 treatment) is implemented only for MP2 energies.
• Exploitation of symmetry of all point groups.
• Can be used sequentially or parallel.
• Can be combined with the COSMO solvation model (see chapter 14 for details). (Presently restricted to sequential calculations.)

Functionality of rimp2:

• Calculation of MP2 energies and/or gradients for RHF and UHF wave functions within the efficient RI-approximation (RI-MP2).
• The frozen core approximation is implemented for both RI-MP2 energies and gradients.
• RI-MP2 needs optimised auxiliary basis sets, which are available for all TURBOMOLE standard basis sets (SVP, TZVP, TZVPP, QZVPP) as well as for the (aug-)cc-p(wC)VXZ (X = D, T, Q, 5) basis sets series (for Al-Ar also for the (aug-)cc-p(wC)V(X+d)Z series).
• Exploitation of symmetry of all point groups.
• Can only be used for sequential calculations.
• Can be combined with the COSMO solvation model (see chapter 14 for details).

Functionality of ricc2:

• Includes most of the above rimp2 functionalities with the exception that it can not (yet) be used with the COSMO solvation model.
• Runs sequentially and parallel (with MPI or OpenMP) and supports at the MP2 level all point groups and can in geometry optimizations and vibrational frequency calculations (with NumForce) combined with RI-JK-SCF for the Hartre-Fock reference calculation.
• Contains an implementation of explicitly correlated MP2-F12 methods (presently restricted to energies and the C₁ point group).
• Can for open-shell calculations be used with UHF and single-determinant high-spin ROHF reference wavefunctions. (ROHF-MP2 presently limited to energies.)
• Energies and gradients for the spin-component scaled SCS- and SOS-MP2 approaches, including a Laplace-transformed implementation of SOS-MP2 with $\cal {O}$($\cal {N}$⁴) scaling computation costs.
• See Chapter 9 for further details.