| 1. |
- Niklasson, Anders M. N., et al.
(författare)
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Extended Lagrangian Born-Oppenheimer molecular dynamics with dissipation
- 2009
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Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:21, s. 148075-
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Tidskriftsartikel (refereegranskat)abstract
- Stability and dissipation in the propagation of the electronic degrees of freedom in time-reversible extended Lagrangian Born-Oppenheimer molecular dynamics [Niklasson , Phys. Rev. Lett. 97, 123001 (2006); Phys. Rev. Lett. 100, 123004 (2008)] are analyzed. Because of the time-reversible propagation the dynamics of the extended electronic degrees of freedom is lossless with no dissipation of numerical errors. For long simulation times under "noisy" conditions, numerical errors may therefore accumulate to large fluctuations. We solve this problem by including a dissipative external electronic force that removes noise while keeping the energy stable. The approach corresponds to a Langevin-like dynamics for the electronic degrees of freedom with internal numerical error fluctuations and external, approximately energy conserving, dissipative forces. By tuning the dissipation to balance the numerical fluctuations the external perturbation can be kept to a minimum.
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| 2. |
- Zheng, Guishan, et al.
(författare)
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Implementation and Benchmark Tests of the DFTB Method and Its Application in the ONIOM Method
- 2009
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 109:9, s. 1841-1854
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Tidskriftsartikel (refereegranskat)abstract
- We present the theoretical and implementation details of the DFTB method with analytical gradients into the Gaussian package. SCF optimization performance with DIIS method is compared with modified Broyden method and Anderson methods, from which DIIS method is to be preferred. The number of geometry optimization steps can be significantly decreased with the Berny algorithm compared to the conjugated gradient method. From the comparison of geometry parameters as well as trends in the change of HOMO and LUMO energies, the results show clearly that DFTB can reproduce values obtained at the B3LYP/6-31G(d) level well. We also investigated the DFTB method as the low level quantum mechanical (QM) method in an ONIOM (QM:QM') description for all amino acid model system and found DFTB promising as a method to describe polarization and charge-transfer effects in large systems.
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| 3. |
- Zheng, Guishan, et al.
(författare)
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Parameter calibration of transition-metal elements for the spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method : Sc, Ti, Fe, Co, and Ni
- 2007
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 3:4, s. 1349-1367
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Tidskriftsartikel (refereegranskat)abstract
- Recently developed parameters for five first-row transition-metal elements (M = Sc, Ti, Fe, Co, and Ni) in combination with H, C, N, and O as well as the same metal (M-M) for the spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method have been calibrated. To test their performance a couple sets of compounds have been selected to represent a variety of interactions and bonding schemes that occur frequently in transition-metal containing systems. The results show that the DFTB method with the present parameters in most cases reproduces structural properties very well, but the bond energies and the relative energies of different spin states only qualitatively compared to the B3LYP/SDD+6-31G(d) density functional (DFT) results. An application to the ONIOM(DFT:DFTB) indicates that DFTB works well as the low level method for the ONIOM calculation.
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