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1

Hydrogen storage on graphene sheet: physisorption, diffusion and chemisorbed pathways by first principles calculations

100%

Costanzo F. , Silvestrelli P. L. , Ancilotto F.

Archives of Metallurgy and Materials

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2012

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tom Vol. 57, iss. 4

1075-1080

EN

Hydrogen is frequently touted as the "fuel of the future" because of its huge potential as clean energy source, although the large-scale adoption of this technology has yet to be realized. One of the remaining barriers to the utilization of hydrogen energy is an efficient and inexpensive means of hydrogen storage. In this work we investigate the nature of this process by first principle calculation. In particular, we study the way in which the H2 molecule can interact with graphene sheet through physisorption and chemisorption mechanism. The first mechanism involves the condensation of the hydrogen molecule on the graphene as a result of weak van der Waals forces, while the chemisorption mechanism involves the preliminary dissociation of the H2 molecule and the subsequent reaction of hydrogen atoms with the unsatured C-C bonds to form C-H bonds. To study carefully the possible physisorbed configurations on the graphene sheet, we take in to account van der Waals (vdW) interactions in DFT using the new method (DFT/vdW-WF) recently developed in our group and based on the concept of maximally localized Wannier functions. There are three possible way in which the H2 molecule can adapt to the structure of graphene: the hollow, the bridge and the top site called H, B and T configurations, respectively. We find the hollow site to be most stable physisorbed state with a binding energy of -50 meV. This value, in agreement with experimental results, is also compared with other vdW-correction methods as described in the following paper. Diffusion of the physisorbed configurations on the graphene sheet and activated reaction pathways in which the molecule starts from a physisorbed configuration to end up in a chemisorbed configurations have also been studied.

PL

Ze względu na możliwość magazynowania wodoru na arkuszu grafenu, badamy nature tego procesu metoda obliczeń ab initio. Cząsteczka H2 może oddziaływać z grafenem na dwa sposoby: fizykosorpcje i chemisorpcje. Mechanizm fizykosorpcji polega na kondensacji cząsteczki wodoru na grafenie na skutek słabych oddziaływań van der Waalsa, podczas gdy mechanizm chemisorpcji polega na wstępnej dysocjacji cząsteczki H2 i następnie reakcji atomów wodoru z niewysyconymi wiązaniami C-C co umożliwia tworzenie wiązań C-H. W celu zobrazowania mechanizmu fizykosorpcji cząsteczek H2 na arkuszu grafenu, analizujemy oddziaływania van der Waalsa (vdW) stosujac teorie funkcjonału gestości (DFT) za pomocą nowej metody (DFT/vdW-WF) niedawno opracowanej w naszej grupie na podstawie koncepcji maksymalnie zlokalizowanych funkcji Wanniera. Analizujemy możliwość absorpcji w różnych miejscach siatki grafenu i orientacje cząsteczki H2 w stosunku do płaszczyzny siatki grafenu. Najbardziej stabilnym miejscem fizykosorbcji jest wnętrze pierścienia grafenu z energia wiązania -50 meV. Wartość ta, zgodna z wynikami doświadczeń, jest także porównywana wartości uzyskanych innymi metodami korekcji vdW. Typowe bariery energetyczne charakteryzujące ścieżkę dyfuzji, są rzędu ∼10 meV. Sytuacja jest inna, gdy cząsteczki wodoru pokonują barierę energetyczna i chemisorbują jako jeden atom wodoru na powierzchni grafenu. Bariery energetyczne w tym przypadku wynoszą około 2-3 eV, w zależności od wybranej ścieżki reakcji.

2

First-principles study of optical properties in Ca-doped ZnO alloys

100%

Bai L.-N. , Lian J.-S. , Zheng W.-T. , Jiang Q.

Open Physics

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2012

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tom 10

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nr 5

1144-1149

EN

Various electronic and optical properties of Zn1−x CaxO ternary alloys of wurtzite structure are calculated using a first-principles approach based on the framework of the generalized gradient approximation to density-functional theory. In particular, on-site Coulomb interactions are introduced, which can reasonably well predict the electronic properties and band gaps of the Zn1−x CaxO (0≤x≤0.25) system. The imaginary part of the calculated dielectric function indicates that the optical transition between O 2p states in the valence band and Zn 4s states in the conduction band shifts to the high-energy range as the Ca concentration increases. The calculated band gap shows a significant increase with increasing Ca concentration. Therefore, Zn1−x CaxO ternary alloys may be a potential candidate alloy for optoelectronic materials, and especially for light-emitters and detectors.

3

First principles study of structure, electronic and optical properties of Y3Fe5O12 in cubic and trigonal phases

100%

Shen T. , Hu C. , Dai H. , Yang W. , Liu H. , Wei X.

Materials Science Poland

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2015

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tom Vol. 33, No. 1

169--174

EN

First principles calculations have been performed to investigate the structure, electronic and optical properties of Y3Fe5O12. Both the cubic and trigonal phases have been considered in our calculation. The calculated structural parameters are slightly larger than the experimental values. The band structures show that Y3Fe5O12 in cubic and trigonal phases have direct band gaps of 0.65 and 0.17 eV. The calculations of dielectric function, absorption, extinction coefficient, refractive index, energy loss function and reflectivity are presented.

4

Electronic structures of Hg-doped anatase TiO2 with different O vacancy concentrations

100%

Zheng S. K. , Wu G. , Zhang S. , Su J. , Liu L.

Materials Science Poland

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2014

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tom Vol. 32, No. 1

93--97

EN

The electronic structures of Hg-doped anatase TiO2 with different O vacancy concentrations were calculated using the first-principles based on the density functional theory. The calculated results show that the forbidden band widths of Hgdoped anatase TiO2 widened along with the increase of O vacancy concentration, which is responsible for the blue shift in the absorption edges. It can be deduced from the present study that the Hg-doped TiO2 samples prepared in the experimental research contain a certain quantity of O vacancies.

5

First-Principles Calculation of Cr/S Co-doped Rutile TiO2

100%

Li J. , Wu F. , Shi J. , Ma L. , Yan X. , Yang N. , Ding B. , Zheng S.

Materials Science Poland

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2020

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tom Vol. 38, No. 2

253--262

EN

The electronic structures and optical properties of pure, Cr, S single- and Cr/S co-doped rutile TiO2 were calculated by the first-principle plane wave pseudopotential method based on density functional theory. The calculated results indicate that the three different doping ways can lead to lattice distortion in the rutile TiO2 and introduce local electronic states in the forbidden band of TiO2. The local energy levels in the forbidden band of TiO2 are mainly contributed by Cr-3d and S-3p orbital. Compared with pure TiO2, the absorption edges (i.e. the edge of the main peak) of the doped TiO2 have different blue shifts; however, the light response ranges of the doped systems are extended, especially in the case of Cr single- and Cr/S co-doped TiO2. The extension of the visible light response range of the doped TiO2 may enhance its visible light photocatalytic performance. In addition, the co-doped TiO2 has a stronger oxidation ability, which may increase the catalytic efficiency of TiO2.

6

First principles molecular dynamics simulations for amorphous HfO2 and Hf1-xSixO2 systems

88%

Ikeda M. , Kresse G. , Nabatame T. , Toriumi A.

Materials Science Poland

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2005

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tom Vol. 23, No. 2

401--406

EN

Amorphous phases of HfO2 and Hf1-xSixO2 were obtained using the Projector Augmented Plane Wave method through the melt and quench technique. For the pure HfO2 system, several pore channels appear in the structures. Changes to x in the Hf1-xSixO2 were also studied. As the concentration of Si increases, the size of the pore channels increases, much space appears and two- fold oxygen atoms increase. By calculating the heat of formation energy, it was found that phase separation between amorphous HfO2 and SiO2 occurs at x> 0.1.

7

First-principles study of atomic structure and electronic properties of Si and F doped anatase TiO2

88%

Li H. , Chen L. , Liu S. , Li C. , Meng J. , Wang Z.

Materials Science Poland

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2015

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tom Vol. 33, No. 3

549--554

EN

Chemical doping represents one of the most effective ways in engineering electronic structures of anatase TiO2 for practical applications. Here, we investigate formation energies, geometrical structures, and electronic properties of Si-, F-doped and Si/F co-doped anatase TiO2 by using spin-polarized density functional theory calculation. We find that the co-doped TiO2 is thermodynamically more favorable than the Si- and F-doped TiO2. Structural analysis shows that atomic impurity varies crystal constants slightly. Moreover, all the three doped systems show a pronounced narrowing of band gap by 0.33 eV for the F-doped TiO2, 0.17 eV for the Si-doped TiO2, and 0.28 eV for the Si/F-co-doped TiO2, which could account for the experimentally observed redshift of optical absorption edge. Our calculations suggest that the Si/F-co-doping represents an effective way in tailoring electronic structure and optical properties of anatase TiO2.

8

A theoretical investigation on the electron structures of Al-based intermetallic compounds

88%

He Y. , Zhi W. , Rong C.

Archives of Metallurgy and Materials

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2013

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tom Vol. 58, iss. 4

1023--1027

EN

Theoretical investigations were performed to study on alloying stability, and electronic structure of (AlCu3, AlCu2Zr and AlZr3). The results show that the lattice parameters obtained after full relaxation of crystalline cells are consistent with experimental data, and these intermetallics have a strong alloying ability and structural stability due to the negative formation energies and the cohesive energies. The further analysis find out that single-crystal elastic constants at zero-pressure satisfy the requirement of mechanical stability for cubic crystals. The calculations on Poisson’s ratio show that AlCu3 is much more anisotropic than the other two intermetallics. In addition, calculations on densities of states indicates that the valence bonds of these intermetallics are attributed to the valence electrons of Cu 3d states for AlCu3, Cu 3d and Zr 4d states for AlCu2Zr, and Al 3s, Zr 5s and 4d states for AlZr3, respectively; in particular, the electronic structure of the AlZr3 shows the strongest hybridization.

PL

Przeprowadzono teoretyczne badania stabilności stopów i struktury elektronowej AlCu3. AlCu2Zr i AlZr3). Obliczania wskazują, że parametry sieci uzyskane po pełnej relaksacji komórek krystalicznych są zgodne z danymi eksperymentalnymi. Związki międzymetaliczne wykazują silną zdolność tworzenia stopów i stabilność strukturalną z powodu ujemnej energii tworzenia i energii spójności. Dalsze analizy wykazały, że stałe elastyczności pojedynczych kryształów przy zerowym ciśnieniu spełniają wymóg stabilności mechanicznej kryształów regularnych. Obliczenia współczynnika Poissona pokazują, że A1Cu3 posiada znacznie bardziej anizotropowe własności niż dwie pozostałe fazy międzymetaliczne. Ponadto, obliczenia gęstości stanów wskazują, że w tworzeniu faz międzymetalicznych biorą udział elektrony walencyjne odpowiednio: Cu na powłoce 3d dla A1Cu3. Cu na 3d i Zr na 4d dla AlCu2Zr. oraz Al na 3s, Zr na 5s i 4d dla AIZr3), w szczególności struktura elektronowa AlZr3) wykazuje najsilniejszą hybrydyzację.

9

Od Humovy teze k etickému univerzalismu

75%

Peroutka D.

Filosofický časopis (Philosophical Journal)

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2015

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tom 63

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nr 4

539-560

EN

The defence of ethical universalism can be grounded in assertion that discussion, if it is to be meaningful, assumes the validity of some minimal agreement in principles. If, however, it is a fundamental fact that the participators in the discussion of ethical questions are (at least potentially) all people, then the principles of that discussion will have universal validity. Hume’s Law, which in this study is examined in detail and precisely formulated, does not allow us to seek a generally valid basis for ethical discussion exclusively in the domain of factual assumptions. This means that the universal validity of some basic evaluative ethical principles must be recognised.

10

The Three Faces of the Cogito: Descartes (and Aristotle) on Knowledge of First Principles

51%

Miles M.

Roczniki Filozoficzne

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2020

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tom 68

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nr 2

63-86

EN

With the systematic aim of clarifying the phenomenon sometimes described as “the intellectual apprehension of first principles,” Descartes’ first principle par excellence is interpreted before the historical backcloth of Aristotle’s Posterior Analytics. To begin with, three “faces” of the cogito are distinguished: (1) the proto-cogito (“I think”), (2) the cogito proper (“I think, therefore I am”), and (3) the cogito principle (“Whatever thinks, is”). There follows a detailed (though inevitably somewhat conjectural) reconstruction of the transition of the mind from (1) via (3) to (2) and back again to (3). What emerges is, surprisingly, a non-circular, non-logical, and ultimately non-mysterious process by which first principles implicitly contained in a complex intuition are gradually rendered explicit (and, if abstract, grasped in their abstract universality). This process bears a striking family resemblance to that intuitive induction (“grasping the universal in the particular”) which Aristotle scholars have distinguished from empirical forms of induction.

PL

Descartes (i Arystoteles) o poznaniu pierwszych zasad W celu systematycznego wyjaśnienia zjawiska określanego niekiedy jako “intelektualne ujęcie pierwszych zasad” przedstawiam interpretację pierwszej zasady Kartezjusza na historycznym tle Analityk wtórych Arystotelesa. Najpierw wyróżniam trzy „oblicza” cogito: (1) proto-cogito („myślę”), (2) właściwe cogito („myślę, więc jestem”) i (3) cogito jako ogólną zasadę („cokolwiek myśli, jest”). Następnie przedstawiam szczegółową (opartą w pewnej mierze na przypuszczeniach) rekonstrukcję w jaki sposób umysł przechodzi z (1) za pośrednictwem (3) do (2) i z powrotem do (3). Dzięki tej rekonstrukcji, co zaskakujące, otrzymujemy niekolisty, pozalogiczny i ostatecznie wcale nie zagadkowy proces stopniowego uwyraźniania pierwszych zasad zawartych domyślenie w złożonej intuicji, przy czym zasady abstrakcyjne są uchwytywane w ich abstrakcyjnej uniwersalności. Proces ten wykazuje uderzające podobieństwo do intelektualnej indukcji („wydobywanie treści ogólnej z tego, co jednostkowe”), którą kontynuatorzy Arystotelesa odróżniali od czysto empirycznych form indukcji.