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1.
《Journal of Molecular Liquids》2006,123(2-3):61-67
Pattern and dynamics of hydrogen bonds in liquid water were investigated by a quantum mechanical/molecular mechanical molecular dynamics (QM/MM MD) simulation at Hartree–Fock (HF) level of theory. A large subregion of the whole system comprising two complete coordination shells was treated quantum mechanically in order to include all polarization and charge transfer effects and to obtain accurate data about structure and dynamics of the intermolecular bonds. The results of this investigation are in agreement with recent experimental findings and suggest that in liquid water every molecule forms in average 2.8, but almost as a rule less than four intermolecular hydrogen bonds. 相似文献
2.
Quantum Boltzmann equation solved by Monte Carlo method for nano-scale semiconductor devices simulation 总被引:1,自引:0,他引:1
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A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC)
method for solving the quantum Boltzmann equation, including collision
broadening and quantum potential corrections, is developed to extend the MC
method to the study of nano-scale semiconductor devices with obvious quantum
mechanical (QM) effects. The quantum effects both in real space and momentum
space in nano-scale semiconductor devices can be simulated. The effective
mobility in the inversion layer of n and p channel MOSFET is simulated and
compared with experimental data to verify this method. With this method 50nm
ultra thin body silicon on insulator MOSFET are simulated. Results indicate
that this method can be used to simulate the 2D QM effects in semiconductor
devices including tunnelling effect. 相似文献
3.
H. Elabidi S. Sahal-Bréchot N. Ben Nessib 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(1):51-64
Quantum mechanical results for the electron impact Stark widths of the 3s–3p transitions in ten Li-like ions from C IV to
P XIII are carried out. The atomic structure is obtained through a
scaled Thomas-Fermi-Dirac-Amaldi potential (SST numerical code) with relativistic corrections. The distorted wave method is
used for the calculation of the S-Matrix, and Feshbach resonances are included by means of the Gailitis method. A comparison with other theoretical and available
experimental results is done. Except for Ne VIII, we find that the agreement between our quantum results and the experiments
gets better when Z increases, which is not the case for the available
close-coupling quantum ones. The behavior of the Stark width with the charge Z and the electron temperature Te is also studied and in contrast to previous studies, an improved agreement
with experimental Z-scaling is obtained. We show that the relative difference between widths of the two fine structure lines
of the same multiplet increases with Z from 0.5% for C IV to
about 12% for P XIII, proving the increasing importance of fine structure effects. The importance of the Feshbach resonances
is discussed and a comparison with available semi-classical perturbation results is given. 相似文献
4.
Electronic properties of model quantum-dot structures in zero and finite magnetic fields 总被引:1,自引:0,他引:1
H. Saarikoski E. Räsänen S. Siljamäki A. Harju M.J. Puska R.M. Nieminen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):241-252
We have computed electronic structures and total energies of circularly confined two-dimensional quantum dots and their lateral
dimers in zero and finite uniform external magnetic fields using different theoretical schemes: the spin-density-functional
theory (SDFT), the current-and-spin-density-functional theory (CSDFT), and the variational quantum Monte Carlo (VMC) method.
The SDFT and CSDFT calculations employ a recently-developed, symmetry-unrestricted real-space algorithm allowing solutions
which break the spin symmetry. Results obtained for a six-electron dot in the weak confinement limit and in zero magnetic
field as well as in a moderate confinement and in finite magnetic fields enable us to draw conclusions about the reliability
of the more approximative SDFT and CSDFT schemes in comparison with the VMC method. The same is true for results obtained
for the two-electron quantum dot dimer as a function of inter-dot distance. The structure and role of the symmetry-breaking
solutions appearing in the SDFT and CSDFT calculations for the above systems are discussed.
Received 16 October 2001 and Received in final form 17 January 2002 相似文献
5.
6.
The Monte Carlo simulation is performed to investigate the quantum
mechanical (QM) effects on heat generation in nano-scale metal oxide
semiconductor field effect transistors (MOSFETs) by solving the
quantum Boltzmann equation. The influence of QM effects both in real
space and $K$ space on the heat generation is investigated. 相似文献
7.
A. Mabrouk 《Journal of Physics and Chemistry of Solids》2010,71(9):1225-1235
The present investigation explored theoretically the geometry structures, the electronic and the optical properties of new benzothiazole derivatives with incorporated triphenylamine/diphenylnaphthylamine or (4-vinylphenyl)acrylonitrile as highly efficient emitting molecular materials for organic light emitting diodes (OLEDs). This study is accomplished in order to provide an in-depth understanding of the structure-properties correlation and their effects on optoelectronic devices.In this contribution, we apply quantum-chemical methods (semiempirical Austin Model 1 (AM1), ab-initio Hartree-Fock (HF) and density functional theory (DFT)) to elucidate the photophysical properties of these molecules. First of all, the geometry structures of these compounds in the ground and the excited states were fully optimized, showing a non-planar configuration structures. Whereas, the geometrical structure of benzothiazole with cyano-PV unit is more planar. Structural parameters and vibrational properties of these compounds are then derived. Moreover, absorption and luminescence properties, lying in a bluish white or red light emission, were elucidated by ZINDO/S methods. The molecular orbital (highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)), the ionization potentials (IPs) and the electron affinities (EAs) of compounds under study were also investigated. It was found that the detailed results obtained from theoretical simulations are consistent with the available experimental data. This kind of theoretical approach has been proved to be reliable for the structure and spectroscopic properties, and predicts the favorable qualities of these benzothiazole derivatives, which make them as the materials of choice for high performance applications. 相似文献
8.
A combination of the best available theoretical techniques for energetics, dynamics, and thermodynamics is employed in an extensive study of Si(n) ( n = 20,25) clusters. For T = 0 we solve the electronic structure by the density functional and the highly accurate quantum Monte Carlo approaches. Finite temperature and dynamical effects are investigated by the ab initio molecular dynamics method. This combination of methods enables us to find several new low-energy isomers and to explain the differences in properties, behavior, and stability of elongated versus compact types of structures and to elucidate the origin of the existing discrepancies between theory and experiments. 相似文献
9.
This paper presents the results of a theoretical study of the structure of the liquidvapor interface of gallium, based on density functional pseudopotential representation of the electron-ion and the ion-ion interactions, and self-consistent quantum Monte Carlo simulation. These predictions of the bulk pair correlation function and the longitudinal density distribution are in very good agreement with the results of recent experimental studies. 相似文献
10.
11.
Chiral liquid crystals have been investigated by means of a multicanonical Monte Carlo approach in order to characterize their phase behaviour by microcanonical equilibrium properties. The liquid crystals were described by three-dimensional lattice systems with intermolecular interactions given by the chiral Lebwohl-Lasher potential. Self-determined boundary conditions have been applied in order to enable the formation of chiral phases with equilibrium pitch. Selected thermodynamic properties, e.g. microcanonical entropy, temperature, heat capacity and a set of order parameters have been determined with dependence on microcanonical total energy. A cholesteric phase with temperature-induced helix inversion could be proven where the helical superstructure of the single component system studied changed its handedness through an infinite-pitch system. The thermodynamical behaviour in the microcanonical ensemble was found to be very similar to the behaviour in the canonical ensemble. The study of microcanonical equilibrium properties by means of multicanonical Monte Carlo simulations was shown to be a powerful tool for the study of the phase behaviour of model liquid crystals. 相似文献
12.
C. Di Paola E. Bodo F. A. Gianturco 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):377-385
Calculations of the quantum structures describing the initial
solvation shells of bosonic helium atoms around a polar, ionic
system like LiH+ are reported, together with the corresponding
quantum energies. The calculations were carried out using the
Diffusion Monte Carlo (DMC) approach and parametric trial functions.
Its final radial and angular distributions for clusters of varying
size are analysed and discussed. The solvation of this ionic dopant
is shown to occur in a way which is strongly affected by the
orientational induction forces between the latter molecule and the
solvent atoms, indicating the onset of “snowball" structures
at the location of the dopant and the clear distinction
between “heliophilic" and “heliophobic" regions of microsolvation. 相似文献
13.
Z. Kuntová Z. Chvoj M. C. Tringides M. Yakes 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):61-66
The growth of Pb islands on a Si(111) surface exhibits many interesting properties. For example, the self-assembled process
results in a homogeneous distribution of Pb islands with uniform height. The dependence of this height on coverage and temperature
can be expressed as a phase diagram [1]. In this paper we develop a model of the growth process that reflects the main features
of the experimental observations and determines the key processes of quantum dot formation in a Pb/Si(111) system. The growth
of islands is simulated by the Monte Carlo method. With suitably chosen parameters the model is able to reconstruct the phase
diagram, via the dependence of the dynamics of Pb atoms on area and height. These dependencies are attributed to stress energy
and quantum size effects. 相似文献
14.
X. Liu Q. Lu P. Liu M. Zhao Z. Wang M. Ying F. Li L. Qin 《Applied Physics A: Materials Science & Processing》2003,76(2):273-275
Range distributions for bismuth ions implanted in AgGaSe2 in the energy range 80–300 keV were investigated by using 2.1-MeV He2+ Rutherford backscattering spectrometry (RBS). A convolution calculation method was used to extract the true distributions
of bismuth from the measured RBS spectra. The range distribution parameters, Rp and ΔRp, were obtained and compared with those obtained from Monte Carlo simulation. The experimental Rp values agree with the Monte Carlo simulation values very well, but the experimental ΔRp values are systematically larger than those from the theoretical simulation.
Received: 28 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002
RID="*"
ID="*"Corresponding author. Fax: +86-531/856-5167, E-mail: xdliu@sdu.edu.cn 相似文献
15.
Caffarel M Hernández-Lamoneda R Scemama A Ramírez-Solís A 《Physical review letters》2007,99(15):153001
Fixed-node diffusion quantum Monte Carlo (FN-DMC) calculations are performed to obtain the most accurate dissociation barrier and heat of formation with respect to dissociation into molecular oxygen for the chemically bound tetraoxygen molecule. Multireference trial wave functions were used and built from truncated CASSCF(16,12) through a weight-consistent scheme allowing to control the fixed-node error. Results are compared with the previous ab initio benchmark Complete Active Space SCF Averaged Coupled Pair Functional/aug-cc-pVQZ (CASSCF-ACPF/AVQZ) results. The FN-DMC barriers to dissociation and heat of formation obtained are 11.6+/-1.6 kcal/mol and 98.5+/-1.9 kcal/mol, respectively. These thermochemical energies should be taken as the theoretical references when discussing the relevance of tetraoxygen in a variety of experiments and atmospheric chemical processes. 相似文献
16.
M. Rehn S. Bergkvist A. Rosengren R. Saers M. Zelán E. Lundh A. Kastberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):223-230
A phase transition for bosonic atoms in a two-dimensional anisotropic optical lattice is considered. If the tunnelling rates
in two directions are different, the system can undergo a transition between a two-dimensional superfluid and a one-dimensional
Mott insulating array of strongly coupled tubes. The connection to other lattice models is exploited in order to better understand
the phase transition. Critical properties are obtained using quantum Monte Carlo calculations. These critical properties are
related to correlation properties of the bosons and a criterion for commensurate filling is established. 相似文献
17.
A force field has been developed to describe the phase behaviour, interfacial, and transport properties of nitrogen and hydrocarbon mixtures under conditions relevant to those found in the high pressure extraction of oil from underground reservoirs. A Gibbs ensemble Monte Carlo method is used to parametrize intermolecular potentials for the pure components by matching experimental and simulated liquid and vapour coexisting densities. Also the surface tension, diffusion coefficient and shear viscosity of nitrogen and its mixtures with butane have been determined. The latter properties were obtained by canonical molecular dynamics simulations. The diffusion coefficient and shear viscosity were calculated by a Green-Kubo method. Results for pure nitrogen are given for temperatures ranging from 70 K to 110K. For mixtures of nitrogen with butane, results are presented at 339.4 K and 380.2 K. Good agreement is found between the results of simulations and available experimental data. 相似文献
18.
19.
Zhi-Dong Zhang 《Physics letters. A》2008,372(4):498-509
A nematic liquid crystal slab composed of N molecular layers is investigated using a simple cubic lattice model, based upon the molecular pair potential which is spatially anisotropic and dependent on elastic constants of liquid crystals. A perfect nematic order is assumed in the theoretical treatment, which means the orientation of the molecular long axis coincides with the director of liquid crystal and the total free energy equals to the total interaction energy. We present a modified Gruhn-Hess model, which is relative to the splay-bend elastic constant K13. Furthermore, we have studied the free nematic interfacial behavior (intrinsic anchoring) by this model in the assumption of the perfect nematic order. We find that the preferred orientation at the free interface and the intrinsic anchoring strength change with the value of modification, and that the director profile can be determined by the competition of the intrinsic anchoring with external forces present in the system. Also we simulate the intrinsic anchoring at different temperatures using Monte Carlo method and the simulation results show that the intrinsic anchoring favors planar alignment and the free interface is more disordered than the bulk. 相似文献
20.
《Superlattices and Microstructures》2000,27(2-3):191-206
Two critical aspects of the MOS scaling towards sub-100 nm gate length are addressed: the gate tunneling and capacitance modeling, and optimization of shallow source/drain (S/D) extension junction to minimize the series resistance. Both advanced physics (quantum mechanics or QM) and practical solution (circuit simulation) are used to tackle the modeling approach. Good results have been obtained compared to available experimental data, validating the hierarchical methodology used in this paper. A hybrid, semi-analytical QM model for channel carrier profile and an accurate direct tunneling model have been developed. An nMOS transistor with effective channel length of 0.08 micron has been analyzed to demonstrate the methodology proposed. 相似文献