<i>ExtSym</i>: a program to aid space-group determination from powder diffraction data

Markvardsen, Anders J.; Shankland, Kenneth; David, William I. F.; Johnston, John C.; Ibberson, R. M.; Tucker, Matthew G.; Nowell, Harriott; Griffin, Tom

doi:10.1107/s0021889808031087

Cited by 31 publications

(26 citation statements)

References 17 publications

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“…The Bruker D8 Advance diffractometer was equipped with a LynxEye detector. The data indexed to a monoclinic cell ( a = 33.543 Å, b = 7.866 Å, c = 5.983 Å, β = 90.35°, and V = 1578.6 Å 3 ), were Pawley fitted in DASH and then the most probable space group of P 2 1 / c determined by use of ExtSym . Consideration of the cell volume, molecular volume, and space group symmetry suggested Z ′ = 0.5.…”

Section: Methodsmentioning

confidence: 99%

Chasing the “Killer” Phonon Mode for the Rational Design of Low‐Disorder, High‐Mobility Molecular Semiconductors

et al. 2019

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The last decade has witnessed drastic improvements of the electronic properties, environmental and operational stability, and processibility of organic semiconductors (OSCs). [1,2] Designing new materials with high carrier mobilities, μ, remains one of the main research objectives to enable faster operation and lower power consumption of circuits and addressing of advanced liquid crystal and organic lightemitting diode displays. [1,3] Yet despite exploring a wide range of material systems, charge carrier mobilities in excess of 10 cm 2 V −1 s −1 have only been achieved in very few molecular semiconductors and highly aligned polymers. [4][5][6] At present, despite significant general advances in the comprehension of transport physics, a Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron-phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high-mobility molecular semiconductors, state-of-the-art quantum mechanical simulations of the vibrational modes and the ensuing electronphonon coupling constants are combined with experimental measurements of the low-frequency vibrations using inelastic neutron scattering and terahertz time-domain spectroscopy. In this way, the long-axis sliding motion is identified as a "killer" phonon mode, which in some molecules contributes more than 80% to the total thermal disorder. Based on this insight, a way to rationalize mobility trends between different materials and derive important molecular design guidelines for new high-mobility molecular semiconductors is suggested.

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Section: Methodsmentioning

confidence: 99%

Chasing the “Killer” Phonon Mode for the Rational Design of Low‐Disorder, High‐Mobility Molecular Semiconductors

et al. 2019

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“…Reflection overlap, background definition and impurity peaks can hamper the correct identification of the space group. A Bayesian approach has been proposed by Markvardsen et al (2001Markvardsen et al ( , 2008 for estimating the probabilities of the different extinction symbols; more recently, for the same purpose, Altomare, Caliandro, Camalli, Cuocci, da Silva et al (2004) developed an automatic method, now included in EXPO2009. It may be summarized as follows: (a) a full pattern decomposition process is carried out by taking into account the space group having the largest Laue symmetry (compatible with the geometry of the crystal system) and no extinction conditions (e.g.…”

Section: Space-group Determination In Expo2009mentioning

confidence: 99%

EXPO2009: structure solution by powder data in direct and reciprocal space

Camalli²,

et al. 2009

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The program EXPO2009 is the evolution of EXPO2004 [Altomare, Caliandro, Camalli, Cuocci, Giacovazzo, Moliterni & Rizzi (2004). J. Appl. Cryst. 37, 1025–1028]. EXPO2009 performs all the steps of ab initio structure solution by powder data: indexing, space‐group determination, estimation of the reflection integrated intensities, structure solution by direct/Patterson methods and/or by a direct‐space/hybrid approach, and model refinement by the Rietveld technique. New procedures have been introduced in EXPO2009 for enhancing the structure solution process, particularly in the case of low‐resolution data and/or organic compounds, when traditional approaches like direct methods may fail. The EXPO2009 graphical interface has been optimized and made very user friendly.

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“…We address the reader to some selected books and papers for a deeper insight of the role of the Rietveld method in the remaining applications (Young 1993;McCusker et al 1999;David et al 2002;Shin et al 2002;Fitzpatrick and Lodini 2003;Balzar et al 2004;Pecharsky and Zavalij 2005;Kaduk 2007a,b;Dinnebier and Billinge 2008;David and Shankland 2008;Soleimanian and Aghdaee 2008;Markvardsen et al 2008). Finally, new ways of learning are being explored.…”

Section: S W Y Ymentioning

confidence: 99%