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- Chwee, Tsz S, et al.
(author)
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Linear scaling multireference singles and doubles configuration interaction
- 2008
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:22, s. 224106-
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Journal article (peer-reviewed)abstract
- A linear scaling multireference singles and doubles configuration interaction (MRSDCI) method has been developed. By using localized bases to span the occupied and virtual subspace, local truncation schemes can be applied in tandem with integral screening to reduce the various bottlenecks in a MRSDCI calculation. Among these, the evaluation of electron repulsion integrals and their subsequent transformation, together with the diagonalization of the large CI Hamiltonian matrix, correspond to the most computationally intensive steps in a MRSDCI calculation. We show that linear scaling is possible within each step. The scaling of the method with system size is explored with a system of linear alkane chains and we proceed to demonstrate this method can produce smooth potential energy surfaces via calculating the dissociation of trans-6-dodecene (C12H24) along the central C=C bond.
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| 2. |
- Swerts, Ben, et al.
(author)
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Embedding fragment ab initio model potentials in CASSCF/CASPT2 calculations of doped solids : Implementation and applications
- 2008
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In: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 4:4, s. 586-594
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Journal article (peer-reviewed)abstract
- In this article, we present a fragment model potential approach for the description of the crystalline environment as an extension of the use of embedding ab initio model potentials (AIMPs). The biggest limitation of the embedding AIMP method is the spherical nature of its model potentials. This poses problems as soon as the method is applied to crystals containing strongly covalently bonded structures with highly nonspherical electron densities. The newly proposed method addresses this problem by keeping the full electron density as its model potential, thus allowing one to group sets of covalently bonded atoms into fragments. The implementation in the MOLCAS 7.0 quantum chemistry package of the new method, which we call the embedding fragment ab inito model potential method (embedding FAIMP), is reported here, together with results of CASSCF/CASPT2 calculations. The developed methodology is applied for two test problems: (i) the investigation of the lowest ligand field states (2)A(1) and B-2(1) of the Cr(V) defect in the YVO4 crystal and (ii) the investigation of the lowest ligand field and ligand-metal charge transfer (LMCT) states at the Mn(II) substitutional impurity doped into CaCO3. Comparison with similar calculations involving AIMPs for all environmental atoms, including those from covalently bounded units, shows that the FAIMP treatment of the YVO4 units surrounding the CrO43- cluster increases the excitation energy B-2(1) -> (2)A(1) by ca. 1000 cm(-1) at the CASSCF level of calculation. In the case of the Mn(CO3)(6)(10-) cluster, the FAIMP treatment of the CO32- units of the environment give smaller corrections, of ca. 100 cm(-1), for the ligand-field excitation energies, which is explained by the larger ligands of this cluster. However, the correction for the energy of the lowest LMCT transition is found to be ca. 600 cm(-1) for the CASSCF and ca. 1300 cm(-1) for the CASPT2 calculation.
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