Tag: DFT
| Authors: |
Thomas Bogaerts, Louis Vanduyfhuys, Danny E. P. Vanpoucke, Jelle Wieme,
Michel Waroquier, Pascal van der Voort and Veronique van Speybroeck |
| Journal: |
Cryst. Eng. Comm. 17(45), 8612-8622 (2015) |
| doi: |
10.1039/c5ce01388g |
| IF(2015): |
3.849 |
| export: |
bibtex |
| pdf: |
<Cryst.Eng.Comm.> |
 |
| Graphical Abstract: Which model represents the experimental XRD-spectra best? Ferromagnetic or anti-ferromagnetic chains? With of without offset? |
The structural characterization of complex crystalline materials such as metal organic frameworks can prove a very difficult challenge both for experimentalists as for theoreticians. From theory, the flat potential energy surface of these highly flexible structures often leads to different geometries that are energetically very close to each other. In this work a distinction between various computationally determined structures is made by comparing experimental and theoretically derived X-ray diffractograms which are produced from the materials geometry. The presented approach allows to choose the most appropriate geometry of a MIL-47(V) MOF and even distinguish between different electronic configurations that induce small structural changes. Moreover the techniques presented here are used to verify the applicability of a newly developed force field for this material. The discussed methodology is of significant importance for modelling studies where accurate geometries are crucial, such as mechanical properties and adsorption of guest molecules.
Permanent link to this article: https://dannyvanpoucke.be/paper2015_xrd_crystendcomm-en/
| Authors: |
Danny E. P. Vanpoucke, Jan W. Jaeken, Stijn De Baerdemacker, Kurt Lejaeghere
and Veronique Van Speybroeck |
| Journal: |
Beilstein J. Nanotechnol. 5, 1738-1748 (2014) |
| doi: |
10.3762/bjnano.5.184 |
| IF(2014): |
2.670 |
| export: |
bibtex |
| pdf: |
<Beilstein> (open access) |
 |
| Graphical Abstract: The MIL-47(V) MOF has one unpaired electron per V site. As a result, different spin configurations are possible, several of which lead to an anti-ferromagnetic state. The spin density of an antiferromagnetic state, containing only ferromagnetic chains is shown on the left. On the right, the electronic band structure of the same system is presented. |
The geometric and electronic structure of the MIL-47(V) metal-organic framework (MOF) is investigated by using ab initio density functional theory (DFT) calculations. Special focus is placed on the relation between the spin configuration and the properties of the MOF. The ground state is found to be antiferromagnetic, with an equilibrium volume of 1554.70 Å3. The transition pressure of the pressure-induced large-pore-to-narrow-pore phase transition is calculated to be 82 MPa and 124 MPa for systems with ferromagnetic and antiferromagnetic chains, respectively. For a mixed system, the transition pressure is found to be a weighted average of the ferromagnetic and antiferromagnetic transition pressures. Mapping DFT energies onto a simple-spin Hamiltonian shows both the intra- and inter-chain coupling to be antiferromagnetic, with the latter coupling constant being two orders of magnitude smaller than the former, suggesting the MIL-47(V) to present quasi-1D behavior. The electronic structure of the different spin configurations is investigated and it shows that the band gap position varies strongly with the spin configuration. The valence and conduction bands show a clear V d-character. In addition, these bands are flat in directions orthogonal to VO6 chains, while showing dispersion along the the direction of the VO6 chains, similar as for other quasi-1D materials.
Permanent link to this article: https://dannyvanpoucke.be/paper2014_mil47beil-en/
