| 1. |
- Kongsted, J, et al.
(författare)
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Coupled cluster and density functional theory studies of the vibrational contribution to the optical rotation of (S)-propylene oxide
- 2006
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 128:3, s. 976-982
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Tidskriftsartikel (refereegranskat)abstract
- In a previous study (Chemical Physics Letters 2005, 401, 385) we computed the optical rotatory dispersion of (S)-propylene oxide in gas phase and solution using the hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3. Even for the highly correlated CC3 model combined with a flexible basis set, the theoretical gas-phase specific rotation at 355 nm was found to be negative in contrast to the experimental result. We argued that vibrational contributions could be crucial for obtaining a complete understanding of the experimental result. Here, we show that this indeed is the case by using coupled cluster models and density functional theory methods to calculate the vibrational contributions to the gas-phase specific rotation at 355, 589.3, and 633 nm. While density functional theory (B3LYP and SAOP functionals) overestimates the specific rotation at 355 nm by approximately 1 order of magnitude and yields an incorrect sign at 589.3 and 633 nm, the coupled cluster results are in excellent agreement with the experimentally measured optical rotations. We find that all vibrational modes contribute significantly to the optical rotation and that temperature effects must be taken into account.
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| 2. |
- Kongsted, J, et al.
(författare)
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Dipole and quadrupole moments of liquid water calculated within the coupled cluster/molecular mechanics method
- 2002
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Ingår i: Chemical Physics Letters. - 0009-2614. ; 364:3-4, s. 379-386
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Tidskriftsartikel (refereegranskat)abstract
- We present the first study of dipole and quadrupole moments of liquid water calculated using coupled cluster/molecular mechanics (COMM) methods. CUMM methods are used to calculate the total dipole moment of the water dimer and the results are compared to the corresponding ab initio quantum mechanical calculations. For liquid water we find that the introduction of polarization effects are very important for an accurate determination of dipole and quadrupole moments. Furthermore, we find that neglecting the correlation effects in the quantum mechanical part of the system leads to an overestimation of the interaction between the two sub-systems.
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| 3. |
- Kongsted, Jacob, et al.
(författare)
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The QM/MM approach for wavefunctions, energies and response functions within self-consistent field and coupled cluster theories
- 2002
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 100:11, s. 1813-1828
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the coupled cluster/molecular mechanics (CC/MM) and self-consistent field/molecular mechanics (SCF/MM) approaches for wavefunctions, energies and response properties. Two physically different theories are derived, the mean-field and the direct-field interaction approaches, together with expressions for the optimization condition of both variational and non-variational wavefunctions and energies. Also derived are the linear response functions at the CC/MM and SCF/MM levels of theory, and the expressions are compared with the vacuum response functions.
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| 4. |
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| 5. |
- Olsen, L, et al.
(författare)
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Electric field gradients of water: A systematic investigation of basis set, electron correlation, and rovibrational effects
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 116:4, s. 1424-1434
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Tidskriftsartikel (refereegranskat)abstract
- Electric field gradients at the oxygen and hydrogen nuclei of water have been calculated using high level ab initio methods. Systematic studies of basis set truncation errors have been carried out at the Hartree-Fock and coupled cluster singles and doubles (CCSD) levels using extended correlation consistent basis sets with up to 398 basis functions. Correlation effects are investigated using a hierarchy of correlation methods extending up to the approximate inclusion of triples excitations by means of the CCSD(T) method. Rovibrational effects have been calculated combining accurate ab initio electric field gradient data and accurate experimental force fields. On the basis of the most accurate results for the electric field gradients, the nuclear quadrupole coupling constants for deuterium and oxygen-17 have been discussed including the temperature dependence. The final results are discussed in view of existing experimental data. Our best values for the nuclear quadrupole coupling constants are in excellent agreement (within 1%) of recent experimental results, while some earlier experimental values are shown to be less reliable. (C) 2002 American Institute of Physics.
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