Molpro (available at http://www.molpro.net) is a general-purpose quantum chemical program. The original focus was on high-accuracy wave function calculations for small molecules, but using local approximations combined with explicit correlation treatments, highly accurate coupled-cluster calculations are now possible for molecules with up to approximately 100 atoms. Recently, multireference correlation treatments were also made applicable to larger molecules. Furthermore, an efficient implementation of density functional theory is available.

Molpro: a general-purpose quantum chemistry program package

The correlation‐consistent polarized valence basis sets (cc‐pVXZ) for the atoms boron through neon have been extended to treat core and core‐valence correlation effects. Basis functions were added to the existing cc‐pVXZ sets to form correlation‐consistent polarized core‐valence sets (cc‐pCVXZ) in the usual pattern: Double zeta added (1s1p), triple zeta added (2s2p1d), quadruple zeta added (3s3p2d1f), and quintuple zeta added (4s4p3d2f1g). The exponents of the core functions were determined by minimizing the difference between all‐electron and valence‐only correlation energies obtained from HF+1+2 calculations on the ground states of the atoms. With the cc‐pCVXZ sets, core, core‐valence, and valence correlation energies all converge exponentially toward apparent complete basis set (CBS) limits, as do the corresponding all‐electron singles and doubles CI energies. Several test applications of the new sets are presented: The first two ionization potentials of boron, the 3P–5S separation in carbon, and the X...

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Gaussian basis sets for use in correlated molecular calculations. V. Core-valence basis sets for boron through neon

An accurate description of the electrical properties of atoms and molecules is critical for quantitative predictions of the nonlinear properties of molecules and of long‐range atomic and molecular interactions between both neutral and charged species. We report a systematic study of the basis sets required to obtain accurate correlated values for the static dipole (α1), quadrupole (α2), and octopole (α3) polarizabilities and the hyperpolarizability (γ) of the rare gas atoms He, Ne, and Ar. Several methods of correlation treatment were examined, including various orders of Moller–Plesset perturbation theory (MP2, MP3, MP4), coupled‐cluster theory with and without perturbative treatment of triple excitations [CCSD, CCSD(T)], and singles and doubles configuration interaction (CISD). All of the basis sets considered here were constructed by adding even‐tempered sets of diffuse functions to the correlation consistent basis sets of Dunning and co‐workers. With multiply‐augmented sets we find that the electrical properties of the rare gas atoms converge smoothly to values that are in excellent agreement with the available experimental data and/or previously computed results. As a further test of the basis sets presented here, the dipole polarizabilities of the F− and Cl− anions and of the HCl and N2 molecules are also reported.

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Gaussian basis sets for use in correlated molecular calculations. IV. Calculation of static electrical response properties

The IMOMM, IMOMO, and ONIOM methods have been proven to be powerful tools for the theoretical treatment of large molecular systems where different levels of theory are applied to different parts of a molecule. Within this framework we present a modified handling of the link atoms which are introduced to terminate the dangling bonds of the model system. Using this new scheme the definition of the combined energy gradient, the Hessian matrix, and the integration of higher derivatives of the energy with respect to nuclear coordinates and the electric field vector becomes straightforward. This allows for the first time the consistent combination of vibrational frequencies and the calculation of other molecular properties such as IR intensities, Raman intensities as well as dipole moments, polarizabilities, and hyperpolarizabilities. Test calculations for some typical as well as unusual examples and partitioning schemes are presented to demonstrate the power and limitations of the method and to provide guidelines for its applicability. Users of the method are strongly advised to test, calibrate and confirm for themselves the validity of the method combination and the model subsystem for the properties they want to calculate.

A new oniom implementation in gaussian98. part i. the calculation of energies, gradients, vibrational frequencies and electric field derivatives

The coupled cluster method restricted to single and double excitations (CCSD) is considered for the case of a spin restricted Hartree–Fock open shell reference determinant. A spin–orbital based formulation, in which the cluster operator spans exactly the minimal first order interacting space, is presented, and computationally optimal working equations are given. In the limit of a large number of closed shell orbitals, the cost is identical to that of an optimum treatment of an equivalent closed shell problem, which is obtained as a special case of the formulation presented. The theory is applied to the calculation of a number of diatomic potential energy functions and compared with spin‐unrestricted theory.

Coupled cluster theory for high spin, open shell reference wave functions

A comparison of the efficiency and accuracy of the quadratic configuration interaction (QCISD), coupled cluster (CCSD), and Brueckner coupled cluster (BCCD) methods

The closed‐shell coupled cluster theory restricted to single and double excitation operators (CCSD) is formulated in a basis of nonorthogonal local correlation functions. Excitations are made from localized molecular orbitals into subspaces (domains) of the local basis, which strongly reduces the number of amplitudes to be optimized. Furthermore, the correlation of distant electrons can be treated in a simplified way (e.g., by MP2) or entirely neglected. It is demonstrated for 20 molecules that the local correlation treatment recovers 98%–99% of the correlation energy obtained in the corresponding full CCSD calculation. Singles‐doubles configuration interac‐ tion (CISD), quadratic configuration interaction (QCISD), and Mo/ller–Plesset perturbation theory [MP2, MP3, MP4(SDQ)] are treated as special cases.

Local treatment of electron correlation in coupled cluster theory

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Claudia Hampel

Papers

Coupled cluster theory for high spin, open shell reference wave functions

A comparison of the efficiency and accuracy of the quadratic configuration interaction (QCISD), coupled cluster (CCSD), and Brueckner coupled cluster (BCCD) methods

Local treatment of electron correlation in coupled cluster theory

Erratum: “Coupled cluster theory for high spin, open shell reference wave functions” [ J. Chem. Phys. 99, 5219 (1993)]