| 1. |
- Aquilante, Francesco, et al.
(författare)
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Modern quantum chemistry with [Open]Molcas
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:21
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Tidskriftsartikel (refereegranskat)abstract
- MOLCAS/OpenMolcas is an ab initio electronic structure program providing a large set of computational methods from Hartree-Fock and density functional theory to various implementations of multiconfigurational theory. This article provides a comprehensive overview of the main features of the code, specifically reviewing the use of the code in previously reported chemical applications as well as more recent applications including the calculation of magnetic properties from optimized density matrix renormalization group wave functions.
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| 2. |
- Karlström, Gunnar, et al.
(författare)
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MOLCAS : a program package for computational chemistry
- 2003
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 28:2, s. 222-239
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Tidskriftsartikel (refereegranskat)abstract
- The program system MOLCAS is a package for calculations of electronic and structural properties of molecular systems in gas, liquid, or solid phase. It contains a number of modern quantum chemical methods for studies of the electronic structure in ground and excited electronic states. A macromolecular environment can be modeled by a combination of quantum chemistry and molecular mechanics. It is further possible to describe a crystalline material using model potentials. Solvent effects can be treated using continuum models or by combining quantum chemical calculations with molecular dynamics or Monte-Carlo simulations. MOLCAS is especially adapted to treat systems with a complex electronic structure, where the simplest quantum chemical models do not work. These features together with the inclusion of relativistic effects makes it possible to treat with good accuracy systems including atoms from the entire periodic system. MOLCAS has effective methods for geometry optimization of equilibria, transition states, conical intersections, etc. This facilitates studies of excited state energy surfaces, spectroscopy, and photochemical processes.
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| 3. |
- Ruiperez, Fernando, et al.
(författare)
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The 5f(3) manifold of the free-ion U3+ : Ab initio calculations
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 434:1-3, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- The energy levels of the 5f(3) manifold of the free-ion U3+ Up to 30 000 cm(-1) are calculated with two well stabilized ab initio methods based on the two-component Hamiltonians of Cowan-Griffin-Wood-Boring and Douglas-Kroll-Hess. Although the corresponding experimental data do not exist, estimates made out of experiments on the 50 manifold of U3+ in solids are usually referred to as the experimental energies of U3+ in gas phase. On the basis of a discussion on the available data of f-element ions in gas phase and in solids and a discussion on the expected precision of the present calculations, we suggest that the 50 energy levels of free U3+ are higher than the estimates and lower than the present ab initio calculations.
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| 4. |
- Swerts, Ben, et al.
(författare)
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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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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 4:4, s. 586-594
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Wåhlin, Pernilla, 1968-
(författare)
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Theoretical Actinide Chemistry – Methods and Models
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemistry of actinides in aqueous solution is important, and it is essential to build adequate conceptual models and develop methods applicable for actinide systems. The complex electronic structure makes benchmarking necessary. In the thesis a prototype reaction of the water exchange reaction for uranyl(VI), for both ground and luminescent states, described with a six-water model, was used to study the applicability of density functional methods on actinides and different solvation models. An excellent agreement between the wave function methods CCSD(T) and MP2 was obtained in the ground state, implying that near-minimal CASPT2 can be used with confidence for the reaction in the luminescent state of uranyl(VI), while density functionals are not suited to describe energetics for this type of reaction. There was an ambiguity concerning the position of the waters in the second hydration sphere. This issue was resolved by investigating a larger model, and prop- erly used the six-water model was found to adequately describe the water exchange reaction. The effect of solvation was investigated by comparing the results from conductor-like polarizable continuum models using two cavity models. Scattered numbers made it difficult to determine which solvation model to use. The final conclusion was that the water exchange reaction in the luminescent state of uranyl(VI) should be addressed with near-minimal CASPT2 and a solvation model without explicit cavities for hydrogens. Finally it was shown that no new chemistry appears in the luminescent state for this reaction. The thesis includes a methodological investigation of a multi-reference density functional method based on a range separation of the two-electron interaction. The method depends on a universal parameter, which has been determined for lighter elements. It is shown here that the same parameter could be used for actinides, a prerequisite for further development of the method. The results are in that sense promising.
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