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1

Kinetics of Polymorphic Transitions in Energetic Compounds

Chukanov N. V., Zakharov V. V., Korsunskiy B. L., Chervonnyi A. D., Vozchikova S. A.

Central European Journal of Energetic Materials

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2016

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Vol. 13, no. 2

483--504

EN

Available data on the kinetics of polymorphic transitions (PTs) in energetic compounds under isothermal conditions are summarized and discussed. It is shown that the general kinetic regularities of these processes (stepwise and continuous regimes) depend on their topotactic mode (frontal or quasi-homogeneous, respectively). In reverse PTs, a nucleation stage is not observed, which is explained by the presence of nuclei of the low-temperature polymorph in the preheated sample. The influence of mechanical effects on the kinetics of PTs in molecular crystals is discussed.

2

Application of genetic algorithms to model the structure of molecular crystals

Łużny W., Czarnecki W.

Polimery

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2014

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T. 59, nr 7-8

542--548

EN

In the case of complex organic molecules, very often happens that the powder diffraction pattern shows only few crystalline reflections and therefore powerful methods like the Rietveld procedure cannot work properly. Then in order to find the model of the structure, for which the calculated diffraction pattern shows an acceptable agreement with the experimental data, one may use one of the "artificial intelligence” techniques. Among them, the genetic algorithms (GA) method is one of the most widely used in a variety of scientific problems. Our idea was to use the unit cell (with its atoms content) as a phenotype of the GA. Each individual represents a random crystal structure. Its genotype contains: lattice constants: a, b and c, lattice angles: a, b, and g, and orientation of molecule vs. the crystallographic axes. Its diffraction pattern is calculated and compared with the reference data. We have prepared a computer program named CrystalFinder. In its present shape, the CrystalFinder program is able to reproduce the crystalline structure of simple "toy” molecular crystals built of molecules containing up to ca twenty atoms. Usually 200—300 generations are sufficient to get a very good agreement between the reference diffraction pattern and the diffractogram obtained by the program as the best fitted individual. It follows that genetic algorithms can be used to model the structure of molecular crystals and more complex systems containing macromolecules.

PL

W przypadku złożonych cząsteczek organicznych bardzo często zdarza się, że dyfraktogram proszkowy ma tylko kilka refleksów krystalicznych i z tego powodu metody modelowania typu Rietvelda nie dają poprawnych wyników. W celu znalezienia modelu struktury, który pozwoli na obliczenie dyfraktogramu wykazującego dobrą zgodność z danymi doświadczalnymi, można zastosować jedną z technik tzw. sztucznej inteligencji. Metoda algorytmów genetycznych (GA) — szeroko stosowana do rozwiązywania rozmaitych problemów naukowych — jest jedną z takich technik. Nasz pomysł polegał na użyciu komórki elementarnej wraz z zawartymi w niej atomami jako osobnika (fenotypu) występującego w GA. Każdy taki osobnik reprezentuje przypadkową strukturę krystaliczną. Jego chromosom (genotyp) zawiera: stałe sieci a, b i c, kąty sieciowe a, b i g, oraz orientację cząsteczki względem osi krystalograficznych. Dla każdego osobnika obliczany jest jego dyfraktogram, który następnie zostaje porównany z danymi referencyjnymi. Idea ta wykorzystana została w napisanym przez nas programie CrystalFinder. W swojej obecnej wersji, program CrystalFinder jest w stanie poprawnie odtworzyć złożoną strukturę krystalograficzną prostego kryształu molekularnego, zbudowanego z molekuł zawierających do ok. dwudziestu atomów. Zwykle przeliczenie 200—300 pokoleń wystarcza do otrzymania dobrej zgodności pomiędzy dyfraktogramem referencyjnym, a dyfraktogramem uzyskanym dla najlepiej dostosowanego osobnika w populacji. Z przeprowadzonych obliczeń wynika, że algorytmy genetyczne mogą być zastosowane do modelowania struktury kryształów molekularnych i bardziej złożonych układów, zawierających również makrocząsteczki.

3

On Relative Stability of Selected Hard Tetramer Solids

Kowalik M., Tretiakov K. V., Wojciechowski K. W.

Computational Methods in Science and Technology

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2010

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Vol. 16, No. 2

141-146

EN

The Einstein crystal method was used to determine free energy differences between some crystalline structures of hard, homonuclear tetramers. The tetramers, each built of four identical hard spheres centered on vertices of a regular tetrahedron of sides equal to the sphere diameter, were arranged in such a way that the spheres formed the fcc lattice at close packing. Various sample sizes were studied and the results were extrapolated to the thermodynamic limit. It was found that the simplest structure of the tetramers, a simple cubic lattice of molecular mass centres with all the molecules having the same orientation, shows the highest free energy amongst the studied ones. The most stable structure of the studied ones was also found.

4

Effects of Strong Inter-hydrogen Bond Dynamical Couplings in the Polarized IR Spectra of trans-beta-Hydromuconic Acid Crystals

Flakus H. T., Jabłońska M., Tyl A.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 5

869-886

EN

This paer presents the re sults of in ves ti ga tions of po lar ized IR spec tra of trans-beta hydromuconic acid (HMA) crystals. The spectra were measured by a transmission method using polarized light at room temperature and at 77 K for three different crystalline faces. Theoretical analysis of the results concerned linear dichroic effects, H/D iso topic and temperature effects observed in the spectra of the hydrogen and deuterium bonds in HMA crystals at the frequency ranges of the ni O–H and the ni O–D bands. The basic crystal spectral properties could be sat is factorily interpreted in a quantitative way for a centrosymmetric cyclic hydrogen bond dimer model. Model calculations, performed within the limits of the “strong-coupling” model, al lowed for quantitative interpretation and for the under standing of the basic properties of the hydrogen bond IR spectra of HMA crystals including H/D isotopic, temperature and dichroic effects. Such a model explains not only the two-branch structure of the ni O–H and ni O–D bands in crystalline spectra, but also some essential linear dichroic effects in the band frequency ranges measured for isotopically diluted HMA crystals. In the scope of our studies the mechanism of H/D isotopic “self-organization” processes, taking place in the crystal hydrogen bond lattices, was also studied. It was proved that for isotopically diluted crystalline samples of HMA, a non-random distribution of protons and deuterons occurs exclusively in the hydrogen bond dimers. Never the less, these dynamical co-operative inter actions between the hydrogen bonds do not in volve of the adjacent hydrogen bond dimers in each unit cell. The two-branch fine structure pattern of the ni O–H and ni O–D bands was ascribed to the vibronic mechanism of vibra tional di pole se lec tion rule break ing for IR tran si tions in centrosymmetric hy dro gen bond dimers. The lin ear dichroic ef fect, dif fer en ti at ing properties of the two op po site spec tral branches of the nO–H and nO–D bands, was also discussed.

5

Investigation of Polarized Infrared Spectra of the Hydrogen Bond in Molecular Crystls. New Spectra Effects in the Vibrational Spectroscopy of Hydrogen Bonded Systems

Flakus H.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 5

489-517

EN

Areview of the experimental as well as of the theoretical studies, performed on the area of the infrared spectroscopy of hydrogen bonded molecular crystals, is given. Discussion of some physical phenomena is presented, responsible for basic spectral effects registered in the infrared spectra, as breaking of vibrational dipole selection rules in the IR spectra, linear dichroic as well as temperature effects, observed in the frequency range of the proton stretching vibrations. Also some newly recognized H/D isotopic effects for hydrogen bonded systems are presented, deduced from a quantitative analysis of the polarized spectra in the IR, namely the so called isotopic "self-organization" effects and the "long-range" H/D isotopic effects.

6

An effect of activation on electrical properties of aromatic hydrocarbons

Kania S.

Scientific Bulletin. Physics / Lodz University of Technology

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2002

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Vol. 22

31-37

EN

The films of p-quaterphenyl were activated with organic molecules. An effect of superficial activation on conductivity of p-quaterphenyl films was under investigation. It was found that there is the dependence of the conductivity on the time of activation and on the concentration of the vapour. It suggests some potential utilization.

PL

Warstwy p-quaterphenylu aktywowano cząsteczkami organicznymi. Badano wpływ aktywacji powierzchniowej na przewodnictwo warstw p-quaterphenylu. Stwierdzono zależność przewodnictwa od czasu aktywacji i stężenia par. Sugeruje to pewne możliwości utylitarne.