scholarly journals Temperature dependent anomalous fluctuations in water: shift of ≈1 kbar between experiment and classical force field simulations

2019 ◽  
Vol 117 (22) ◽  
pp. 3232-3240 ◽  
Author(s):  
Harshad Pathak ◽  
Alexander Späh ◽  
Katrin Amann-Winkel ◽  
Fivos Perakis ◽  
Kyung Kyung Hwan Kim ◽  
...  
Keyword(s):  
Force Field ◽  
Temperature Dependent ◽  
Water Shift

Strukturuntersuchungen an chiralen Schiff-Basen des 11-cis-Retinals/Structure Investigation of Chiral Schiff Bases of 11-cis-Retinal

1989 ◽  
Vol 44 (3) ◽  
pp. 333-344 ◽  
Author(s):  
Volker Buß ◽  
Verena Haas ◽  
Ute Wingen
Keyword(s):  
Experimental Data ◽  
Force Field ◽  
Schiff Bases ◽  
Structural Information ◽  
Quantitative Agreement ◽  
Uv Spectra ◽  
Structure Investigation ◽  
Temperature Dependent ◽  
Optimized Geometries ◽  
Hydrogen Bonded

CD and UV spectra of four chiral 11-cis-retinal Schiff bases obtained by condensing the aldehyde with asymmetric amines are used to gain structural information about the polyene conformation. The spectra are temperature-dependent indicating the same 12-s-cis/trans equilibrium as in 11-cis-retinal. In addition, CD absorptions arise at lower temperatures whose only origin is the inherent dissymmetric nature of the retinylidene Chromophore. CNDO /S-calculations performed on the basis of force-field optimized geometries give results which can partially be rationalized on the basis of experimental data. Quantitative agreement is obtained in the case of chiral hydrogen-bonded dimers.

scholarly journals Computational Pharmaceutical Materials Science: Beyond Static Structures.

2014 ◽  
Vol 70 (a1) ◽  
pp. C1541-C1541
Author(s):  
Jacco van de Streek ◽  
Kristoffer Johansson ◽  
Xiaozhou Li
Keyword(s):  
Crystal Structure ◽  
Molecular Dynamics ◽  
Force Field ◽  
Crystal Structures ◽  
Structure Prediction ◽  
Force Fields ◽  
Individual Compound ◽  
Crystal Structure Prediction ◽  
Temperature Dependent ◽  
Mechanical Methods

The five Crystal-Structure Prediction (CSP) Blind Tests have shown that molecular-mechanics force fields are not accurate enough for crystal structure prediction[1]. The first--and only--method to successfully predict all four target crystal structures of one of the CSP Blind Tests was dispersion-corrected Density Functional Theory (DFT-D), and this is what we use for our work. However, quantum-mechanical methods (such as DFT-D), are too slow to allow simulations that include the effects of time and temperature, certainly for the size of molecules that are common in pharmaceutical industry. Including the effects of time and temperature therefore still requires molecular dynamics (MD) with less accurate force fields. In order to combine the accuracy of the successful DFT-D method with the speed of a force field to enable molecular dynamics, our group uses Tailor-Made Force Fields (TMFFs) as described by Neumann[2]. In Neumann's TMFF approach, the force field for each chemical compound of interest is parameterised from scratch against reference data from DFT-D calculations; in other words, the TMFF is fitted to mimic the DFT-D energy potential. Parameterising a dedicated force field for each individual compound requires an investment of several weeks, but has the advantage that the resulting force field is more accurate than a transferable force field. Combining crystal-structure prediction with DFT-D followed by molecular dynamics with a tailor-made force field allows us to calculate e.g. the temperature-dependent unit-cell expansion of each predicted polymorph, as well as possible temperature-dependent disorder. This is relevant for example when comparing the calculated X-ray powder diffraction patterns of the predicted crystal structures against experimental data.

(111) Monocrystalline Nickel Films

1972 ◽  
Vol 30 ◽  
pp. 512-513
Author(s):  
T.E. Pratt ◽  
R.W. Vook
Keyword(s):  
Film Thickness ◽  
Deposition Rate ◽  
Room Temperature ◽  
Narrow Range ◽  
High Vacuum ◽  
Residual Pressure ◽  
Temperature Dependent ◽  
Deposition Parameters ◽  
Transmission Electron ◽  
Substrate Temperatures

(111) oriented thin monocrystalline Ni films have been prepared by vacuum evaporation and examined by transmission electron microscopy and electron diffraction. In high vacuum, at room temperature, a layer of NaCl was first evaporated onto a freshly air-cleaved muscovite substrate clamped to a copper block with attached heater and thermocouple. Then, at various substrate temperatures, with other parameters held within a narrow range, Ni was evaporated from a tungsten filament. It had been shown previously that similar procedures would yield monocrystalline films of CU, Ag, and Au.For the films examined with respect to temperature dependent effects, typical deposition parameters were: Ni film thickness, 500-800 A; Ni deposition rate, 10 A/sec.; residual pressure, 10-6 torr; NaCl film thickness, 250 A; and NaCl deposition rate, 10 A/sec. Some additional evaporations involved higher deposition rates and lower film thicknesses.Monocrystalline films were obtained with substrate temperatures above 500° C. Below 450° C, the films were polycrystalline with a strong (111) preferred orientation.

Millimetre-wave and infrared spectroscopy of Br13 CN: anharmonic force field of cyanogen bromide from spectroscopic data and ab initio calculations

1997 ◽  
Vol 90 (3) ◽  
pp. 495-497
Author(s):  
CLAUDIO ESPOSTI ◽  
FILIPPO TAMASSIA ◽  
CRISTINA PUZZARINI ◽  
RICCARDO TARRONI ◽  
ZDENEK ZELINGER
Keyword(s):  
Infrared Spectroscopy ◽  
Force Field ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Spectroscopic Data ◽  
Cyanogen Bromide ◽  
Millimetre Wave ◽  
Anharmonic Force

Molecular force field evaluation by empirical constraints

1976 ◽  
Vol 73 ◽  
pp. 1051-1057
Author(s):  
Sadao Isotani ◽  
Alain J.-P. Alix
Keyword(s):  
Force Field ◽  
Field Evaluation ◽  
Molecular Force ◽  
Molecular Force Field
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