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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the 2D Heisenberg model with S=1/2
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 1999. - Vol. 41, Is. 1. - P103-107. - ISSN 1063-7834, DOI 10.1134/1.1130737
Примечания : Cited References: 33
Предметные рубрики: SQUARE-LATTICE
GROUND-STATE
SPIN-CORRELATIONS
ANTIFERROMAGNET
LA2CUO4
EU2CUO4
ENERGY
ORDER
Аннотация: The two-dimensional (2D) Heisenberg model with anisotropic exchange (Delta=1-J(x)/J(z)) and S=1/2 is investigated by the quantum Monte Carlo method. The energy, susceptibility, specific heat, spin-spin correlation functions, and correlation radius are calculated. The sublattice magnetization (sigma) and the Neel temperature of the anisotropic antiferromagnet are logarithmic functions of the exchange anisotropy: 1/sigma + 1 + 0.13(1) ln(1/Delta). Crossover of the static magnetic structural factor as a function of temperature from power-law to exponential occurs for T(c)/J approximate to 0.4. The correlation radius can be approximated by 1/xi =2.05T(1.0(6))/exp(1.0(4)/ T). For La(2)CuO(4) the sublattice magnetization is calculated as sigma=0.45, the exchange is J=(1125=1305) K; for Er(2)CuO(4)J similar to 625 K and the exchange anisotropy Delta similar to 0.003. The temperature dependence of the static structural magnetic factor and the correlation radius above the Neel temperature in these compounds can be explained by the formation of topological excitations (spinons). (C) 1999 American Institute of Physics. [S1063-7834(99)02401-6].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Sadreev A. F.
Заглавие : Ab-initio investigation of thermoactivated directional transport of hydrogen molecules inside narrow carbon nanotubes
Место публикации : Phys. Status Solidi B. - 2009. - Vol. 246: 23rd Winterschool on Electronic Properties of Novel Materials (MAR 14, 2009, Kirchberg, GERMANY), Is. 11. - P.2598-2601. - ISSN 0370-1972, DOI 10.1002/pssb.200982285
Примечания : Cited References: 21. - A.S.Fedorov thanks the Institute of Computer Modeling (Krasnoyarsk, Russia) and the Joint Supercomputer Center (Moscow) for an assistence in quantum chemical calculations.
Предметные рубрики: DIFFUSION
ENERGY
Аннотация: Using the pseudopotential DFT and the empirical potential methods we calculate the potential acting to the hydrogen molecules in narrow single-wall carbon nanotubes (SWCNT) (6,0),(7,0) and (3,3). The potential forms a goffered potential surface and can be approximated as V(z, r, phi) approximate to V(0) sin(2 pi z/a) + V(r). We show that in these SWCNTs transport of molecules is given mainly by thermoactivated hoppings between minima of the periodic potential along the tube axis. Taking into account that hydrogen density distribution inside nanotube is stationary and assuming the temperature is changed linearly along the SWCNT length we show that the H(2) density is sufficiently variated, especially for the case of (6,0)SWCNT where the density on both SWCNT ends are different at similar to 30 times when the temperature is changed along the SWCNT from 300K to 1200K. Suppose that H2 molecules can penetrate in the both open SWCNT ends, the molecules would move in the direction of the temperature decreasing. This effect may be used potentially to build up a molecular pump driven by the temperature gradient along narrow nanotube. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Ovchinnikov S. G.
Заглавие : Density and thermodynamics of hydrogen adsorbed inside narrow carbon nanotubes
Разночтения заглавия :авие SCOPUS: Density and Thermodynamics of Hydrogen Adsorbed Inside Narrow Carbon Nanotubes
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 3. - P584-589. - ISSN 1063-7834, DOI 10.1134/1.1687883
Примечания : Cited References: 21. - This study was supported by the federal program “Integration,” project no. Б0017
Предметные рубрики: MOLECULAR-DYNAMICS
TRANSITIONS
TRANSPORT
ENERGY
TUBES
Аннотация: A model is proposed for calculating the thermodynamic functions and the equilibrium density of a one-dimensional chain of molecules (atoms) adsorbed inside a narrow nanotube. The model considers both the interaction between introduced atoms (molecules) and their interaction with the nanotube walls. The quantum-mechanical effects resulting in discrete energy levels of a particle and in its smeared position between neighbors are taken into account. In calculating the free energy at a nonzero temperature, the phonon contribution and the particle transitions to excited levels are considered. The model is applied to calculate the thermodynamic parameters of adsorbed hydrogen molecules inside extremely narrow single-wall carbon nanotubes of the (3,3) and (6,0) type. It is shown that external pressure gives rise to a sequence of first-order phase transitions, which change the density of adsorbed hydrogen molecules. (C) 2004 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Avramov P. V., Ovchinnikov S. G., Kresse G.
Заглавие : Isotope velocity differentiation in thin carbon nanotubes through quantum diffusion
Место публикации : Europhys. Lett. - 2003. - Vol. 63, Is. 2. - P.254-260. - ISSN 0295-5075, DOI 10.1209/epl/i2003-00512-5
Примечания : Cited References: 17
Предметные рубрики: MOLECULAR-DYNAMICS
TRANSITIONS
TRANSPORT
ENERGY
Аннотация: An approach is proposed to evaluate the average velocities of adsorbate molecules in one-dimensional nanopore, when quantum tunneling between neighboring potential minima leads to nonzero velocity. The approach is used to calculate the hydrogen isotope molecule (H-2, D-2, T-2) velocities in ultrathin carbon single-wall nanotubes (SWNT) (3, 3) and (6, 0). It is shown that the isotope mass difference leads to large differences of the quantum tunneling value and large differences of the average molecule velocities, especially inside the tube (6, 0). It is shown that different tube chirality leads to drastically different velocities of adsorbate molecules, even if the diameters of both nanotubes do not differ significantly.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Sadreev A. F.
Заглавие : Thermoactivated transport of molecules H-2 in narrow single-wall carbon nanotubes
Коллективы : RFBR [0602-16132]
Разночтения заглавия :авие SCOPUS: Thermoactivated transport of molecules H 2 in narrow single-wall carbon nanotubes
Место публикации : Eur. Phys. J. B: SPRINGER, 2009. - Vol. 69, Is. 3. - P363-368. - ISSN 1434-6028, DOI 10.1140/epjb/e2009-00152-1
Примечания : Cited References: 40. - We are grateful to S. G. Ovchinnikov for discussions. This work has been supported by RFBR grant 0602-16132.
Предметные рубрики: DIFFUSION
NANOPORES
ENERGY
MOTION
FLUIDS
Ключевые слова (''Своб.индексиров.''): hydrogen molecule--inner potential--lennard-jones potential--periodic potentials--plane wave--potential surfaces--single-wall carbon nanotubes--thermal fluctuations--tube walls--carbon nanotubes--hydrogen--molecules--single-walled carbon nanotubes (swcn)
Аннотация: By use both of the plane wave DFT and the empirical exp-6 Lennard-Jones potential methods we calculate the inner potential in narrow single-wall carbon nanotubes (SWCNT) (6, 0), (7, 0) and (3, 3) which affects the hydrogen molecules. The inner potential forms a goffered potential surface and can be approximated as V(z,r,phi)a parts per thousand V(0)sin (2 pi z/a)+V(r). We show that in these SWCNTs transport of molecules is given mainly by thermoactivated hoppings between minima of the periodic potential along the tube axis. The rate hoppings is substantially depends on temperature because of thermal fluctuations of tube wall.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Qiao, Jianwei, Ning, Lixin, Molokeev M. S., Chuang, Yu-Chun, Zhang, Qinyuan, Poeppelmeier, Kenneth R., Xia, Zhiguo
Заглавие : Site-Selective Occupancy of Eu2+ Toward Blue-Light-Excited Red Emission in a Rb3YSi2O7:Eu Phosphor
Место публикации : Angew. Chem. - 2019. - Vol. 131, Is. 33. - P.11645-11650. - ISSN 1521-3757, DOI 10.1002/ange.201905787
Примечания : Cited References: 41. - This work is supported by the National Natural Science Foundation of China (51722202, 51572023, and 11574003), Natural Science Foundations of Beijing (2172036), Fundamental Research Funds for the Central Universities (FRF-TP-18-002C1), and the Guangdong Provincial Science & Technology Project (2018A050506004). K.R.P. recognizes that this work was made possible by support from the National Science Foundation, Solid State Materials Chemistry award DMR-1608218.
Предметные рубрики: LUMINESCENCE PROPERTIES
CE3+
ENERGY
PHOTOLUMINESCENCE
TRANSITION
Аннотация: Establishing an effective design principle in solid-state materials for a blue-light-excited Eu2+-doped red-emitting oxide-based phosphors remains one of the significant challenges for white light-emitting diodes (WLEDs). Selective occupation of Eu2+ in inorganic polyhedra with small coordination numbers results in broad-band red emission as a result of enhanced crystal-field splitting of 5d levels. Rb3YSi2O7:Eu exhibits a broad emission band at λmax=622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu2+ ions preferably occupy RbO6 and YO6 polyhedra and show the characteristic red emission band of Eu2+. The excellent thermal quenching resistance, high color-rendering index Ra (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare-earth phosphors is an effective strategy to target tailored optical performance.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov D.G., Kitaura K., Avramov P. V., Jensen J.H.
Заглавие : Analytic gradient for the adaptive frozen orbital bond detachment in the fragment molecular orbital method
Место публикации : Chem. Phys. Lett. - 2009. - Vol. 477, Is. 1-3. - P.169-175. - JUL 28. - ISSN 0009-2614, DOI 10.1016/j.cplett.2009.06.072
Примечания : Cited Reference Count: 49. - Гранты: We thank Professor M. Suenaga of Kyushu University for continuing his development of the modeling software FACIO and its FMO interface. D. G. F. and K. K. were supported by the a Grant-in- Aid for Scientific Research (JSPS, Japan) and the Next Generation SuperComputing Project, Nanoscience Program (MEXT, Japan). J.H.J. was supported by a Skou Fellowship from the Danish Research Agency (Forskningsradet for Natur og Univers).Финансирующая организация: JSPS, Japan; Next Generation SuperComputing Project; MEXT, Japan; Danish Research Agency
Предметные рубрики: DENSITY-FUNCTIONAL THEORY
GEOMETRY OPTIMIZATIONS
SEMICONDUCTOR NANOWIRES
SILICON NANOWIRES
METHOD FMO
ENERGY
SURFACES
RECONSTRUCTION
CHEMISTRY
PROTEINS
Ключевые слова (''Своб.индексиров.''): energy gradients--fragment molecular orbital methods--future applications--geometry optimization--numerical criteria--silicon nanowires--molecular modeling--molecular orbitals
Аннотация: We have developed and implemented the analytic energy gradient for the bond detachment scheme in the fragment molecular orbital method (FMO) suitable to describe solids, and applied it to the geometry optimization of a silicon nanowire at several levels of theory. In addition, we have examined in detail the effects of the particular choice of the fragmentation upon the accuracy and introduced a number of numerical criteria to characterize the errors. The established route is expected to provide guidance for future applications of FMO to surfaces, solids and nanosystems. (C) 2009 Elsevier B. V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : ZINENKO V. I., FEDOROV A. S.
Заглавие : CALCULATION OF LONG-WAVELENGTH PHONON FREQUENCIES, OF DIELECTRIC PERMITTIVITY, AND B1-B2 PHASE-TRANSITIONS IN ALKALI-METAL HYDRIDES BY THE DENSITY-FUNCTIONAL TECHNIQUE
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1994. - Vol. 36, Is. 5. - P1357-1365. - ISSN 0367-3294
Примечания : Cited References: 17
Предметные рубрики: PRESSURE
ENERGY
WOS
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Qiao, Jianwei, Ning, Lixin, Molokeev M. S., Chuang, Yu-Chun, Zhang, Qinyuan, Poeppelmeier, Kenneth R., Xia, Zhiguo
Заглавие : Site-Selective Occupancy of Eu2+ Toward Blue-Light-Excited Red Emission in a Rb3YSi2O7:Eu Phosphor
Место публикации : Angew. Chem. Int. Edit. - 2019. - Vol. 58, Is. 33. - P.11521-11526. - ISSN 1433-7851, DOI 10.1002/anie.201905787. - ISSN 1521-3773(eISSN)
Примечания : Cited References: 41. - This work is supported by the National Natural Science Foundation of China (51722202, 51572023, and 11574003), Natural Science Foundations of Beijing (2172036), Fundamental Research Funds for the Central Universities (FRF-TP-18-002C1), and the Guangdong Provincial Science & Technology Project (2018A050506004). K.R.P. recognizes that this work was made possible by support from the National Science Foundation, Solid State Materials Chemistry award DMR-1608218.
Предметные рубрики: LUMINESCENCE PROPERTIES
CE3+
ENERGY
PHOTOLUMINESCENCE
TRANSITION
Аннотация: Establishing an effective design principle in solid-state materials for a blue-light-excited Eu2+-doped red-emitting oxide-based phosphors remains one of the significant challenges for white light-emitting diodes (WLEDs). Selective occupation of Eu2+ in inorganic polyhedra with small coordination numbers results in broad-band red emission as a result of enhanced crystal-field splitting of 5d levels. Rb3YSi2O7:Eu exhibits a broad emission band at λmax=622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu2+ ions preferably occupy RbO6 and YO6 polyhedra and show the characteristic red emission band of Eu2+. The excellent thermal quenching resistance, high color-rendering index Ra (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare-earth phosphors is an effective strategy to target tailored optical performance.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Arauzo A., Kazak N. V., Ivanova N. B., Platunov M. S., Knyazev Yu. V., Bayukov O. A., Bezmaternykh L. N., Lyubutin I. S., Frolov K. V., Ovchinnikov S. G., Bartolome J.
Заглавие : Spin-glass behavior in single crystals of hetero-metallic magnetic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4
Коллективы : MINECO Project [MAT11/23791, MAT2014-53921-R], DGA IMANA project [E-34], Russian Foundation for Basic Research [13-02-00958, 13-02-00358, 14-02-31051-mol-a], Council for Grants of the President of the Russian Federation [NSh-2886.2014.2, SP-938.2015.5], program of Foundation for Promotion of Small Enterprises in Science and Technology ("UMNIK" program)
Место публикации : J. Magn. Magn. Mater.: Elsevier Science, 2015. - Vol. 392. - P.114-125. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2015.05.006. - ISSN 18734766(eISSN)
Примечания : Cited References:36. - This work has been financed by the MINECO Project MAT11/23791, MAT2014-53921-R and DGA IMANA project E-34, Russian Foundation for Basic Research (project Nr. 13-02-00958, 13-02-00358 and 14-02-31051-mol-a), Council for Grants of the President of the Russian Federation (project Nr. NSh-2886.2014.2 and SP-938.2015.5). The work of one of coauthors (M.S.P.) was supported by the program of Foundation for Promotion of Small Enterprises in Science and Technology ("UMNIK" program).
Предметные рубрики: SYSTEMS
CHAIN
Fe
SUSCEPTIBILITY
Fe2OBO3
ENERGY
Ключевые слова (''Своб.индексиров.''): warwickites--spin glass--entanglement--exchange interaction
Аннотация: Magnetic properties of heterometallic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 are presented, highlighting the effect of Co substitution on the magnetic properties of these compounds. The analysis of magnetization and heat capacity data has shown that these compounds exhibit a spin-glass transition below TSG=10, 20 and 22 K, respectively. Using zero field ac susceptibility as entanglement witness we find that the low dimensional magnetic behavior above TSG show quantum entanglement behavior χ(Τ)∝T−α(Τ) up to TE≈130 K. The α parameters have been deduced as a function of temperature and Co content, indicating the existence of random singlet phase in this temperature region. Above TE the paramagnetism is interpreted in terms of non-entangled spins giving rise to Curie–Weiss paramagnetism. The different intra- and inter-ribbon exchange interaction pathways have been calculated within a simple indirect coupling model. It is determined that the triangular motifs in the warwickite structure, together with the competing interactions, induce frustration. The spin-glass character is explained in terms of the substitutional disorder of the Mg, Fe and Co atoms at the two available crystallographic sites, and the frustration induced by the competing interactions. The Co substitution induces uniaxial anisotropy, increases the absolute magnetization and increases the spin-glass freezing temperature. The entanglement behavior is supported in the intermediate phase irrespective of the introduction of anisotropy by the Co substitution.Представлены магнитные свойства гетерометаллических варвикитов MgFeBO4, Mg0.5Co0.5FeBO4 и CoFeBO4, с выделением эффекта замещения Co на магнитные свойства этих соединений. Анализ данных намагниченности и теплоемкости показал, что эти соединения обладают спин-стекольным переходом ниже TSG=10, 20 и 22 К соответственно. Используя нулевого поля для переменной восприимчивости, мы находим, что низкоразмерных магнитное поведение выше TSG показать квантовая запутанность поведение χ (Τ) αT? α (Τ) до TEE130 К. Параметры α были выведены в зависимости от температуры и содержание Со, что указывает на существование случайного синглетного фазы в этой области температур. Над TE в Парамагнетизм интерпретируется в терминах перепутывания спинов, приводящих к парамагнетизму Кюри-Вейсса. Различные внутри- и обменного взаимодействия между направлениями были рассчитаны в модели простой косвенной связи. Установлено, что треугольные мотивы в структуре варвикита, вместе с конкурирующими взаимодействиями, вызывают фрустрацию. Характер спинового стекла объясняется в условиях беспорядка замещения атомов Mg, Fe и Co в двух доступных кристаллографических позициях, и фрустрацию, индуцированную конкурирующими взаимодействиями. Замена Со вызывает одноосную анизотропию, увеличивает абсолютную намагниченность и повышает температуру замерзания спинового стекла. Запутанность Поведения поддерживается в промежуточной фазе, независимо от анизотропии из-за введения замещения Со.
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