An explicitly correlated local coupled cluster method for calculations of large molecules close to the basis set limit

Abstract

A new explicitly correlated local coupled-cluster method with single and double excitations and a perturbative treatment of triple excitations [DF-LCCSD(T0)-F12x (x = a,b)] is presented. By means of truncating the virtual orbital space to pair-specific local domains (domain approximation) and a simplified treatment of close, weak and distant pairs using LMP2-F12 (pair approximation) the scaling of the computational cost with molecular size is strongly reduced. The basis set incompleteness errors as well as the errors due to the domain approximation are largely eliminated by the explicitly correlated terms. All integrals are computed using efficient density fitting (DF) approximations. The accuracy of the method is investigated for 52 reactions involving medium size molecules. A comparison of DF-LCCSD(T0)-F12x reaction energies with canonical CCSD(T)-F12x calculations shows that the errors introduced by the domain approximation are indeed very small. Care must be taken to keep the errors due to the additional pair approximation equally small, and appropriate distance criteria are recommended. Using these parameters, the root mean square (RMS) deviations of DF-LCCSD(T0)-F12a calculations with triple-ζ basis sets from estimated CCSD(T) complete basis set (CBS) limits and experimental data amount to only 1.5 kJ mol(-1) and 2.9 kJ mol(-1), respectively. For comparison, the RMS deviation of the CCSD(T)/CBS values from the experimental values amounts to 3.0 kJ mol(-1). The potential of the method is demonstrated for five reactions of biochemical or pharmacological interest which include molecules with up to 61 atoms. These calculations show that molecules of this size can now be treated routinely and yield results that are close to the CCSD(T) complete basis set limits.

An efficient local coupled cluster method for accurate thermochemistry of large systems

“…Alternatively, these effects can be accounted for by using the explicitly correlated LCCSD(T0)-F12 method, which is presented in Ref. 1.…”

“…The geometries of these molecules were optimized by DF-LMP2 using the cc-pVTZ basis set. 91 We have studied three reactions involving these molecules, namely, the hydrogenation of progesteron via pregnenolon to pregnanediol (reactions I and II), and the last synthetic step to yield androstendione (reaction III), Moreover, as an illustrative example for the capabilities of our program, we will present some preliminary results on the thermal reaction energy of the photodamaged cyclobutane pyrimidine dimer (CPD) lesion back to the undamaged/repaired dimer (TpT) in the ATTA sequence of the DNA double strand. 92 Further benchmarks, comparing the standard DF-LCCSD(T) method with the explicitly correlated variant DF-LCCSD(T)-F12 are presented in Ref.…”

“…92 Further benchmarks, comparing the standard DF-LCCSD(T) method with the explicitly correlated variant DF-LCCSD(T)-F12 are presented in Ref. 1.…”

“…The latter problem can be much alleviated by adding terms to the wavefunction that depend explicitly on the inter-electronic distances r 12 (socalled F12-methods). This will be addressed in the companion paper, 1 in which the current work is extended to include such terms. a) Electronic mail: werner@theochem.uni-stuttgart.de.…”

Explicitly correlated plane waves: Accelerating convergence in periodic wavefunction expansions

“…The result are methods which share the intrinsic accuracy of the complete basis set (CBS) limit of their parent method, but which approach this limit far more rapidly, thereby reducing the cost of the method. Combining this with density fitting [48], local approximations [49,50], and multireference methods [51][52][53][54][55][56][57][58][59][60][61][62] has greatly extended the reach of quantum chemistry in recent years.…”