Incremental CCSD(T)(F12)|MP2-F12-A Method to Obtain Highly Accurate CCSD(T) Energies for Large Molecules.

In this work, we apply the recently proposed MP2 correction to incremental energies within the domain-specific basis set approach to incrementally expanded CCSD(T)(F12) energies. The approach is tested for a set of 27 molecules with different electronic structures including water clusters, aqua complexes, aliphatic hydrocarbons, alkenes, alkynes, aromatic systems, and amino acids. The root mean squared deviation of the absolute energies with respect to the standard calculation is 1.7 kJ/mol, the mean absolute deviation is 1.2 kJ/mol, and the range is 4.7 kJ/mol. The wall time of the computations is reduced due to the application of a doubly parallel strategy-the independent coupled cluster calculations are performed on up to 70 nodes in parallel, and in addition the computations on one node are performed with the SMP-parallelized coupled cluster code in TURBOMOLE. Using this strategy, we can perform computations in minutes or hours, instead of days or months. Applying the proposed scheme enables us to routinely treat systems with 50 atoms at the CCSD(T)(F12) level in combination with appropriate basis sets to obtain nearly CBS accuracy. Also, larger systems are still feasible on a standard cluster as demonstrated for H3O(+)(H2O)25Cl(-) with 80 atoms.