| 1. |
- Jiemchooroj, Auayporn, et al.
(författare)
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C6 dipole-dipole dispersion coefficients for the n-alkanes : Test of an additivity procedure
- 2004
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 69:4, s. 044701-1
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Tidskriftsartikel (refereegranskat)abstract
- The dipole-dipole dispersion coefficients for pairs of n-alkane molecules with six or less carbon atoms were studied. The calculations were based on the dynamic polarizabilities of the molecules on the imaginary frequency axis. The dynamic polarizabilities in turn were obtained from Kohn-Sham density-functional theory polarization propagator calculations using the hybrid B3LYP exchange-correlation functional. The results for the static polarizabilities of each molecule were decomposed into bond polarizabilities and values for the polarizabilities of the C-H and C-C bonds.
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| 2. |
- Jiemchooroj, Auayporn, et al.
(författare)
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Complex polarization propagator method for calculation of dispersion coefficients of extended π-conjugated systems: The C6 coefficients of polyacenes and C60
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:12, s. 124312-
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Tidskriftsartikel (refereegranskat)abstract
- The frequency-dependent polarizabilities and the C6 dipole-dipole dispersion coefficients for the first members of the polyacenes namely benzene, naphthalene, anthracene, and naphthacene as well as the fullerene C60 have been calculated at the time-dependent Hartree-Fock level and the time-dependent density-functional theory level with the hybrid B3LYP exchange-correlation functional. The dynamic polarizabilities at imaginary frequencies are obtained with use of the complex linear polarization propagator method and the C6 coefficients are subsequently determined from the Casimir-Polder relation. We report the first ab initio calculations of the C6 coefficients for the molecules under consideration, and our recommended value for the dispersion coefficient of the fullerene is 101.0 a.u.
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| 3. |
- Jiemchooroj, Auayporn, et al.
(författare)
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Electric dipole polarizabilities and C6 dipole-dipole dispersion coefficients for alkali metal clusters and C60
- 2007
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Ingår i: Journal of Computational Methods in Sciences and Engineering. - : Institute of Physics (IOP). - 1472-7978 .- 1875-8983. ; 7:5-6, s. 475-488
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Tidskriftsartikel (refereegranskat)abstract
- The frequency dependent polarizabilities of closed-shell alkali metal clusters containing up to ten lithium, potassium, and rubidium atoms have been calculated using the linear complex polarization propagator approach in conjunction with Hartree-Fock and Kohn-Sham density functional theory. In combination with polarizabilities for C-{60} from a previous work [J. Chem. Phys. 123, 124312 (2005)], the C-6 dipole-dipole dispersion coefficients for the metal cluster-to-cluster and cluster-to-buckminster fullerene interactions are obtained via the Casimir-Polder relation. The B3PW91 results for the polarizabilities and dispersion interactions of the alkali metal dimers and tetramers are benchmarked against couple cluster calculations, and the whole series of calculations are compared against the corresponding work on sodium clusters [J. Chem. Phys. 125, 124306 (2006)]. The error bars of the reported theoretical results for the C-6 coefficients are estimated to be 8%. © 2007 - IOS Press and the authors. All rights reserved.
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| 4. |
- Jiemchooroj, Auayporn, et al.
(författare)
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Electric dipole polarizabilities and C6 dipole-dipole dispersion coefficients for sodium clusters and C60
- 2006
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 125:12
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Tidskriftsartikel (refereegranskat)abstract
- The frequency-dependent polarizabilities of closed-shell sodium clusters containing up to 20 atoms have been calculated using the linear complex polarization propagator approach in conjunction with Hartree-Fock and Kohn-Sham density functional theories. In combination with polarizabilities for C 60 from a previous work [J. Chem. Phys. 123, 124312 (2005)], the C6 dipole-dipole dispersion coefficients for the metal-cluster-to- cluster and cluster-to-buckminster-fullerene interactions are obtained via the Casimir-Polder relation [Phys. Rev. 73, 360 (1948)]. The B3PW91 results for the polarizability of the sodium dimer and tetramer are benchmarked against coupled cluster calculations. The error bars of the reported theoretical results for the C6 coefficients are estimated to be 5%, and the results are well within the error bars of the experiment. © 2006 American Institute of Physics.
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| 5. |
- Jiemchooroj, Auayporn, et al.
(författare)
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Electronic circular dichroism spectra from the complex polarization propagator
- 2007
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 126:13
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Tidskriftsartikel (refereegranskat)abstract
- The complex linear polarization propagator approach has been applied to the calculation of electronic circular dichroism spectra of 3R -chloro-1-butyne, 3R -methylcyclopentanone, 3S -methylcyclohexanone, 4R -1,1-dimethyl-[3]-(1,2) ferrocenophan-2-on, S-3,3, 3′, 3′ -tetramethyl- 1, 1′ -spirobi[3H,2,1]-benzoxaselenole, and the fullerene C84. Using time-dependent Kohn-Sham density functional theory, it is shown that a direct and efficient evaluation of the circular dichroism spectrum can be achieved. The approach allows for the determination of the circular dichroism at an arbitrary wavelength thereby, in a common formulation and implementation, covering the visible, ultraviolet, and x-ray regions of the spectrum. In contrast to traditional methods, the entire manifold of excited states is taken into account in the calculation of the circular dichroism at a given wavelength. © 2007 American Institute of Physics.
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| 6. |
- Jiemchooroj, Auayporn
(författare)
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First-principles calculations of long-range intermolecular dispersion forces
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work presents first-principles calculations of long-range intermolecular dispersion energies between two atoms or molecules as expressed in terms of the C6 dipole-dipole dispersion coefficients. In a series of publications, it has been shown by us that the complex linear polarization propagator method provides accurate ab initio and first-principles density functional theory values of the C6 dispersion coefficients in comparison with those reported in the literature. The selected samples for the investigation of dispersion interactions in the electronic ground state are the noble gases, n-alkanes, polyacenes, azabenzenes, and C60. It has been shown that the proposed method can also be used to determine dispersion energies for species in their respective excited electronic states. The C6 dispersion coefficients for the first π → π* excited state of the azabenzene molecules have been obtained with the adopted method in the multiconfiguration self-consistent field approximation. The dispersion energy of the π → π* excited state is smaller r than that of the ground state. It is found that the characteristic frequencies ω1 defined in the London approximation of n-alkanes vary in a narrow range and that makes it possible to construct a simple structure-to-property relation based on the number of -bonds for the dispersion interaction in these saturated compounds. However, this simple approach is not applicable for the interactions of the π-conjugated systems since their characteristic frequencies ω1 vary strongly depending on the systems.
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| 7. |
- Jiemchooroj, Auayporn, 1978-
(författare)
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Long-range intermolecular dispersion forces and circular dichroism spectra from first-principles calculations
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work presents first-principles calculations of long-range intermolecular dispersion energies between two atoms or molecules and of electronic circular dichroism spectra of chiral molecules. The former is expressed in terms of the C6 dipole-dipole dispersion coefficients Δε, and the latter is given in terms of the extinction coefficient. In a series of publications, the complex linear polarization propagator method has been shown to be a powerful tool to provide accurate ab initio and first-principles density functional theory results. This was the case not only for the C6 dispersion coefficients but also for the electronic circular dichroism at an arbitrary wavelength ranging from the optical to the X-ray regions of the spectrum. The selected samples for the investigation of dispersion interactions in the electronic ground state are the noble gases, n-alkanes, polyacenes, azabenzenes, alkali-metal clusters, and C60. It is found that the values of C6 for the sodium-cluster-to-fullerene interactions are well within the error bars of the experiment. The proposed method can also be used to determine dispersion energies for species in their respective excited electronic states. The C6 dispersion coefficients for the first π → π* excited state of the azabenzene molecules have been obtained with the adopted method in the multiconfiguration self-consistent field approximation. The dispersion energy of the π → π* excited state is smaller than that of the ground state. It is found that the characteristic frequencies ω1 defined in the London approximation of n-alkanes vary in a narrow range which makes it possible to construct a simple structure-to-property relationship based on the number of π-bonds for the dispersion interaction in these saturated compounds. However, this simple approach is not applicable to the interactions of the π-conjugated systems since, depending on the systems, their characteristic frequencies ω1 can vary greatly. In addition, an accomplishment of calculations of the electronic circular dichroism spectra in the near-edge X-ray absorption has been demonstrated.
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| 8. |
- Jiemchooroj, Auayporn, et al.
(författare)
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Near-edge x-ray absorption and natural circular dichroism spectra of L-alanine : A theoretical study based on the complex polarization propagator approach
- 2007
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 127:16
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Tidskriftsartikel (refereegranskat)abstract
- The complex polarization propagator method [J. Chem. Phys. 123, 194103 (2005)] has been employed in conjunction with density functional theory and gauge-including atomic orbitais in order to determine the near-edge x-ray absorption and natural circular dichroism spectra of L-alanine in its neutral and zwitterionic forms. Results are presented for the K-edges of carbon, nitrogen, and oxygen. In contrast to traditional methods, the proposed approach enables a direct determination of the spectra at an arbitrary frequency instead of focusing on the rotatory strengths for individual electronic transitions. The propagator includes a complete set of nonredundant electron-transfer operators and allows for full core-hole relaxation. The theoretical spectrum at the nitrogen K-edge of the zwitterion compares well with the experimental spectrum. © 2007 American Institute of Physics.
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| 9. |
- Jiemchooroj, Auayporn, et al.
(författare)
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X-ray absorption and natural circular dichroism spectra of C84 : A theoretical study using the complex polarization propagator approach
- 2008
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:23
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Tidskriftsartikel (refereegranskat)abstract
- The x-ray absorption and circular dichroism K -edge spectra for the D2 -isomer of C84 have been determined using the complex polarization propagator method in conjunction with Kohn-Sham density functional theory. The circular dichroism spectrum is rich in details and, in comparison to the absorption spectrum, it provides a superior resolution of the electronic transitions below the ionization threshold. © 2008 American Institute of Physics.
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| 10. |
- Norman, Patrick, et al.
(författare)
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First principle calculations of dipole-dipole dispersion coefficients for the ground and first π → π∗ excited states of some azabenzenes
- 2004
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Ingår i: Journal of Computational Methods in Sciences and Engineering. - : IOS Press. - 1472-7978 .- 1875-8983. ; 4:3, s. 321-332
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Tidskriftsartikel (refereegranskat)abstract
- The complex polarization propagator method has been applied to the calculation of dipole-dipole dispersion coefficients (also known as C6 coefficients) of pyridine, pyrazine, and s-tetrazine. These calculations refer to the electronic ground states as well as the first excited states of π → π∗ character. It is argued that accurate ground state dispersion coefficients are obtained with density functional theory using the B3LYP exchange-correlation functional. The proposed values for the C6 coefficients of pyridine, pyrazine, and s-tetrazine in their ground states are 1543 a.u., 1398 a.u., and 1014 a.u., respectively. Multi-configurational complete active space calculations are performed on these compounds in their respective π → π∗ excited state. The isotropic averages of the frequency-dependent polarizabilities are smaller in the excited states, but the effective frequencies-defined in the London-van der Waals dispersion relation-are on the other hand larger.
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