High-quality, temperature-dependent terahertz spectroscopy of single crystalline L-alanine: Experiment and density-functional theory

2021 ◽  
Vol 154 (24) ◽  
pp. 244311
Author(s):  
T. J. Sanders ◽  
J. L. Allen ◽  
J. Horvat ◽  
R. A. Lewis
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Terahertz Spectroscopy ◽  
Temperature Dependent ◽  
High Quality ◽  
Functional Theory ◽  
Single Crystalline

scholarly journals Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional theory (DFT-D)

2014 ◽  
Vol 70 (6) ◽  
pp. 1020-1032 ◽  
Author(s):  
Jacco van de Streek ◽  
Marcus A. Neumann
Keyword(s):  
Density Functional Theory ◽  
Crystal Structures ◽  
Powder Diffraction ◽  
Energy Minimization ◽  
Molecular Crystal ◽  
Density Functional ◽  
Powder Diffraction Data ◽  
High Quality ◽  
Functional Theory ◽  
Atomic Coordinates

In 2010 we energy-minimized 225 high-quality single-crystal (SX) structures with dispersion-corrected density functional theory (DFT-D) to establish a quantitative benchmark. For the current paper, 215 organic crystal structures determined from X-ray powder diffraction (XRPD) data and published in an IUCr journal were energy-minimized with DFT-D and compared to the SX benchmark. The on average slightly less accurate atomic coordinates of XRPD structures do lead to systematically higher root mean square Cartesian displacement (RMSCD) values upon energy minimization than for SX structures, but the RMSCD value is still a good indicator for the detection of structures that deserve a closer look. The upper RMSCD limit for a correct structure must be increased from 0.25 Å for SX structures to 0.35 Å for XRPD structures; the grey area must be extended from 0.30 to 0.40 Å. Based on the energy minimizations, three structures are re-refined to give more precise atomic coordinates. For six structures our calculations provide the missing positions for the H atoms, for five structures they provide corrected positions for some H atoms. Seven crystal structures showed a minor error for a non-H atom. For five structures the energy minimizations suggest a higher space-group symmetry. For the 225 SX structures, the only deviations observed upon energy minimization were three minor H-atom related issues. Preferred orientation is the most important cause of problems. A preferred-orientation correction is the only correction where the experimental data are modified to fit the model. We conclude that molecular crystal structures determined from powder diffraction data that are published in IUCr journals are of high quality, with less than 4% containing an error in a non-H atom.

Identifying and explaining vibrational modes of quinacridones via temperature-resolved terahertz spectroscopy: absorption experiments and solid-state density functional theory simulations

2020 ◽  
Vol 22 (35) ◽  
pp. 19672-19679 ◽  
Author(s):  
A. D. Squires ◽  
Adam J. Zaczek ◽  
R. A. Lewis ◽  
Timothy M. Korter
Keyword(s):  
Density Functional Theory ◽  
Solid State ◽  
Density Functional ◽  
Terahertz Spectroscopy ◽  
State Density ◽  
Spectral Features ◽  
Thermal Contraction ◽  
Vibrational Modes ◽  
Functional Theory

New spectral features and anomalous shifting of vibrational modes of beta quinacridone are revealed, unusual thermal contraction the likely origin.

Strong Adsorption of Al-Doped Bilayer Graphene Toward Anticancer Cisplatin

NANO ◽  
2018 ◽  
Vol 13 (06) ◽  
pp. 1850068
Author(s):  
Guo-Qing Li ◽  
Meng Zhang ◽  
Wei Li
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Bilayer Graphene ◽  
Monolayer Graphene ◽  
Hollow Site ◽  
High Quality ◽  
Functional Theory ◽  
Strong Adsorption ◽  
Atom Interaction ◽  
Cl Atom

The adsorption of cisplatin on pristine monolayer graphene (MLG), pristine bilayer graphene (BLG) and Al-doped BLG (Al-BLG) was investigated using density functional theory. The obtained results showed that pristine MLG and pristine BLG were not sensitive to cisplatin. Adsorption energy can be primarily influenced by the atomic species rather than the adsorption position. Moreover, it is strong chemisorption of hollow-site Al-BLG (H-Al-BLG) toward cisplatin. The most stable configurations are the Pt or Cl atom interaction with the Al atom of H-Al-BLG. In conclusion, H-Al-BLG is a kind of potential high quality delivery carrier for anticancer cisplatin.

HELIUM ON NANOPATTERNED SURFACES AT FINITE TEMPERATURE

2010 ◽  
Vol 24 (25n26) ◽  
pp. 4915-4922
Author(s):  
E. S. HERNANDEZ ◽  
F. ANCILOTTO ◽  
M. BARRANCO ◽  
A. HERNANDO ◽  
M. PI
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
Alkali Metal ◽  
Density Functional ◽  
Finite Range ◽  
Temperature Dependent ◽  
Functional Theory ◽  
Infinite Array ◽  
Dependent Density

We investigate the wetting behavior of helium on nanostructured alkali metal surfaces, at temperatures below and slightly above the bulk superfluidity threshold. Starting from a determination of the phase diagram of helium on semiinfinite planar Cs up to 3 K, performed within finite–range, temperature–dependent density functional theory, we examine the modifications of the isotherms introduced by an infinite array of nanocavities. We compare the hysterectic loops of helium on nonwettable Cs surfaces and on wettable Na substrates in the same temperature range.

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