Articles you may be interested inWhat are the most efficient basis set strategies for correlated wave function calculations of reaction energies and barrier heights?Comment on "Calculation of accurate permanent dipole moments of the lowest Σ + 1 , 3 states of heteronuclear alkali dimers using extended basis sets" [J.Basis set convergence studies of Hartree-Fock calculations of molecular properties within the resolution of the identity approximation Calculation of accurate permanent dipole moments of the lowest Σ + 1 , 3 states of heteronuclear alkali dimers using extended basis setsThe convergence of the second-order Møller-Plesset perturbation theory ͑MP2͒ correlation energy with the cardinal number X is investigated for the correlation consistent basis-set series cc-pVXZ and cc-pV(Xϩd)Z. For the aug-cc-pVXZ and aug-cc-pV(Xϩd)Z series the convergence of the MP2 correlation contribution to the dipole moment is studied. It is found that, when d-shell electrons cannot be frozen, the cc-pVXZ and aug-cc-pVXZ basis sets converge much slower for third-row elements then they do for first-and second-row elements. Based on the results of these studies criteria are deduced for the accuracy of auxiliary basis sets used in the resolution of the identity ͑RI͒ approximation for electron repulsion integrals. Optimized auxiliary basis sets for RI-MP2 calculations fulfilling these criteria are reported for the sets cc-pVXZ, cc-pV(Xϩd)Z, aug-cc-pVXZ, and aug-cc-pV(Xϩd)Z with XϭD, T, and Q. For all basis sets the RI error in the MP2 correlation energy is more than two orders of magnitude smaller than the usual basis-set error. For the auxiliary aug-cc-pVXZ and aug-cc-pV(Xϩd)Z sets the RI error in the MP2 correlation contribution to the dipole moment is one order of magnitude smaller than the usual basis set error. Therefore extrapolations towards the basis-set limit are possible within the RI approximation for both energies and properties. The reduction in CPU time obtained with the RI approximation increases rapidly with basis set size. For the cc-pVQZ basis an acceleration by a factor of up to 170 is observed.

Molpro is a general purpose quantum chemistry software package with a long development history. It was originally focused on accurate wavefunction calculations for small molecules but now has many additional distinctive capabilities that include, inter alia, local correlation approximations combined with explicit correlation, highly efficient implementations of single-reference correlation methods, robust and efficient multireference methods for large molecules, projection embedding, and anharmonic vibrational spectra. In addition to conventional input-file specification of calculations, Molpro calculations can now be specified and analyzed via a new graphical user interface and through a Python framework.

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Articles you may be interested inLarge scale polarizability calculations using the approximate coupled cluster model CC2 and MP2 combined with the resolution-of-the-identity approximation Implementation of transition moments between excited states in the approximate coupled-cluster singles and doubles model Calculation of excited-state properties using general coupled-cluster and configuration-interaction models An implementation of transition moments and excited-state first-order properties is reported for the approximate coupled-cluster singles-and-doubles model ͑CC2͒ using the resolution of the identity ͑RI͒ approximation. In parallel to the previously reported code for the ground-and excited-state amplitude equations, we utilize a partitioned form of the CC2 equations and thus eliminate the need to store any N 4 intermediates. This opens the perspective for applications on molecules with 30 and more atoms. The accuracy of the RI approximation is tested for a set of 29 molecules for the aug-cc-pVXZ (XϭD,T,Q) basis sets in connection with the recently optimized auxiliary basis sets. These auxiliary basis sets are found to be sufficient even for the description of diffuse states. The RI error is compared to the usual basis set error and is demonstrated to be insignificant.

We propose a novel explicitly correlated coupled-cluster singles and doubles method CCSD(F12(*)), which retains the accuracy of CCSD-F12 while the computational costs are only insignificantly larger than those for a conventional CCSD calculation.