Effect of P impurity on mechanical properties of NiAl Σ5 grain boundary:From perspectives of stress and energy

In this paper, we employ the first-principle total energy method to investigate the effect of P impurity on mechanical properties of NiAl grain boundary(GB). According to "energy", the segregation of P atom in NiAlΣ5 GB reduces the cleavage energy and embrittlement potential, demonstrating that P impurity embrittles NiAlΣ5 GB. The first-principle computational tensile test is conducted to determine the theoretical tensile strength of NiAlΣ5 GB. It is demonstrated that the maximum ideal tensile strength of NiAlΣ5 GB with P atom segregation is 144.5 GPa, which is lower than that of the pure NiAlΣ5 GB(164.7 GPa). It is indicated that the segregation of P weakens the theoretical strength of NiAlΣ5 GB.The analysis of atomic configuration shows that the GB fracture is caused by the interfacial bond breaking. Moreover, P is identified to weaken the interactions between Al–Al bonds and enhance Ni–Ni bonds.     

Energetics and electronic structure of refractory elements in the dislocation of NiAl

Using DMol and the discrete variational method within the framework of the density functional theory,we study the alloying effects of Nb,Ti,and V in the [100](010) edge dislocation core of NiAl.We find that when Nb(Ti,V) is substituted for Al in the center-Al,the binding energy of the system reduces 3.00 eV(2.98 eV,2.66 eV).When Nb(Ti,V) is substituted for Ni in the center-Ni,the binding energy of the system reduces only 0.47 eV(0.16 eV,0.09 eV).This shows that Nb(Ti,V) exhibits a strong Al site preference,which agrees with the experimental and other theoretical results.The analyses of the charge distribution,the interatomic energy and the partial density of states show that some charge accumulations appear between the impurity atom and Ni atoms,and the strong bonding states are formed between impurity atom and neighbouring host atoms due mainly to the hybridization of 4d5s(3d4s) orbitals of impurity atoms and 3d4s4p orbitals of host Ni atoms.The impurity induces a strong pinning effect on the [100](010) edge dislocation motion in NiAl,which is related to the mechanical properties of the NiAl alloy.     

Collapse–revival of squeezing of two atoms in dissipative cavities

Based on the time-convolutionless master-equation approach, we investigate the squeezing dynamics of two atoms in dissipative cavities. We find that the atomic squeezing is related to initial atomic states, atom–cavity couplings, nonMarkovian effects and resonant frequencies of an atom and its cavity. The results show that a collapse–revival phenomenon will occur in the atomic squeezing and this process is accompanied by the buildup and decay of entanglement between two atoms. Enhancing the atom–cavity coupling can increase the frequency of the collapse–revival of the atomic squeezing.The stronger the non-Markovian effect is, the more obvious the collapse–revival phenomenon is. In particular, if the atom–cavity coupling or the non-Markovian effect is very strong, the atomic squeezing will tend to a stably periodic oscillation in a long time. The oscillatory frequency of the atomic squeezing is dependent on the resonant frequency of the atom and its cavity.     

Effect of element Re on the grain boundary cohesion of α-Fe

The effect of Re segregation on the α-Fe ∑5 [001] （010） grain boundary （GB） is investigated by using a software called DMol and discrete variational method （DVM）. Based on the Rice Wang model, the calculated segregation energy and defect formation energy show that Re is a strong cohesive enhancer. We also calculated the interatomic energy （IE） and bond order （BO） of several atomic pairs to investigate the mechanism of the cohesive effect of Re microscopically and locally. The results show that IEs of atomic pairs formed by those atoms which cross the plane of GB are strengthened due to the segregation of Re, while the BOs of the corresponding pairs are slightly decreased. This discrepancy demonstrates that IE which contains the Hamiltoniaa of interaction between atoms is a good quantity to describe the bonding strength. The analysis suggests that the electronic effect between atomic pair which comes directly from Hamiltonian is the key factor, The charge density is also presented, and the result indicates that the bonding strength between the Fe atoms on the GB is enhanced due to the segregation of Re, which is consistent with the analysis of IE.     

Structures,stabilities,and magnetic properties of the Fe_nAu(n=1-12) clusters

The configurations,stabilities,electronic,and magnetic properties of Fe_nAu(n = 1–12) clusters are investigated systematically by using the relativistic all-electron density functional theory with the generalized gradient approximation.The substitutional effects of Au in Fe_(n+1)(n = 1,2,4,5,10–12) clusters are found in optimized structures which keep the similar frameworks with the most stable Fe_(n+1)clusters.And the growth way for Fe_nAu(n = 6–9) clusters is that the Au atom occupies a peripheral position of Fen cluster.The peaks appear respectively at n = 6 and 9 for Fen Au clusters and at n = 5 and 10 for Fe_(n+1)clusters based on the size dependence of second-order difference of energy,implying that these clusters possess relatively high stabilities.The analysis of atomic net charge Q indicates that the charge always transfers from Fe to Au atom which causes the Au atom to be nearly non-magnetic,and the doped Au atom has little effect on the average magnetic moment of Fe atoms in Fen Au cluster.Finally,the total magnetic moment is reduced by 3 μB for each of Fen Au clusters except n = 3,11,and 12 compared with for corresponding pure Fe_(n+1) clusters.     

Effect of Re on stacking fault nucleation under shear strain in Ni by atomistic simulation

The effect of Re on stacking fault(SF) nucleation under shear strain in Ni is investigated using the climbing image nudged elastic band method with a Ni–Al–Re embedded-atom-method potential. A parameter(?Eb sf), the activation energy of SF nucleation under shear strain, is introduced to evaluate the effect of Re on SF nucleation under shear strain. Calculation results show that ?Eb sfdecreases with Re addition, which means that SF nucleation under shear strain in Ni may be enhanced by Re. The atomic structure observation shows that the decrease of ?Eb sfmay be due to the expansion of local structure around the Re atom when SF goes through the Re atom.     

Adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co （200）： A first-principles density-functional study

First-principles calculations based on density functional theory are used to investigate the adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co(200). The preferred site for the carbon atom on the surface is the hollow site, and the preferred site in the subsurface is the octahedral site. There is charge transfer from the surface to the adsorbed carbon atom, and for the most favorable adsorbed structure the charge transfer is largest. Moreover, the energy barriers for the diffusions of carbon atoms on the surface and from the surface into the subsurface and then back to the surface are calculated in detail. The results indicate that the energy barrier for the diffusion of carbon atoms on the surface is comparable to that from the subsurface to the surface. The results imply that both the direct surface nucleation and the surface segregation from Co bulk can be observed in the chemical vapor deposition growth of graphene on Co(200)substrate, which can gain a new insight into the growth mechanism of graphene.     

A first-principles study of the magnetic properties in boron-doped ZnO

First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Zn1-xBxO (0相似文献   

Re effects in model Ni-based superalloys investigated with first-principles calculations and atom probe tomography

The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.     

Diffusion and thermite reaction process of film-honeycomb Al/NiO nanothermite:Molecular dynamics simulations using ReaxFF reactive force field

The diffusion and thermite reaction process of Al/NiO nanothermite composed of Al nanofilm and NiO nano honeycomb are investigated by molecular dynamics simulations in combination with the Reax FF. The diffusion and thermite reaction are characterized by measuring energy release, adiabatic reaction temperature, and activation energy. Based on time evolution of atomic configuration and mean square displacement, the initialization of the thermite reaction process of Al/NiO nanothermite results from the diffusion of Al atoms. Under the microcanonical ensemble, it is found that the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite reaches over 5500 K, and activation energy is 8.43 k J/mol. The release energy of the thermite reaction process of Al/NiO nanothermite is 2.2 k J/g, which is in accordance with the available experimental value. With the same initial temperature, the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite has a tendency to decrease dramatically as the equivalence ratio increases. On the basis of chemical bond analysis, the initial temperature and equivalence ratio have great effects on the thermite reaction process, but do not significantly affect the average length of Al–Ni nor Al–O bond. Overall, the thermite reaction of film-honeycomb Al/NiO nanothermite is a complicated process instead of a theoretical equation.     

Physical properties of FePt nanocomposite doped with Ag atoms:First-principles study

L10FePt nanocomposite with high magnetocrystalline anisotropy energy has been extensively investigated in the fields of ultra-high density magnetic recording media. However, the order–disorder transition temperature of the nanocomposite is higher than 600℃, which is a disadvantage for the use of the material due to the sustained growth of FePt grain under the temperature. To address the problem, addition of Ag atoms has been proposed, but the magnetic properties of the doped system are still unclear so far. Here in this paper, we use first-principles method to study the lattice parameters,formation energy, electronic structure, atomic magnetic moment and order–disorder transition temperature of L10FePt with Ag atom doping. The results show that the formation energy of a Ag atom substituting for a Pt site is 1.309 eV, which is lower than that of substituting for an Fe site 1.346 eV. The formation energy of substituting for the two nearest Pt sites is2.560 eV lower than that of substituting for the further sites 2.621 eV, which indicates that Ag dopants tend to segregate L10FePt. The special quasirandom structures(SQSs) for the pure FePt and the FePt doped with two Ag atoms at the stable Pt sites show that the order–disorder transition temperatures are 1377℃ and 600℃, respectively, suggesting that the transition temperature can be reduced with Ag atom, and therefore the FePt grain growth is suppressed. The saturation magnetizations of the pure FePt and the two Ag atoms doped FePt are 1083 emu/cc and 1062 emu/cc, respectively,indicating that the magnetic property of the doped system is almost unchanged.     

Density functional theory study of Mg_2Ni_n(n= 1–8) clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin(n = 1–8) clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital(NBO) are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.     

Atomic motion in the magneto–optical trap consisting of partially spatially coherent laser

Rb atom motion in a magneto–optical trap(MOT) consisting of a partially spatially coherent laser(PSCL) is investigated theoretically. The spatial coherence of the laser is controlled by the electro–optic crystal. The instantaneous spatial distribution of the dissipative force induced by the PSCL on an Rb atom is varying with time stochastically. The simulated results indicate that compared with a fully coherent laser, the spatial coherent laser has effects on the atomic trajectories;however, the capture velocity and the escape velocity are kept the same. The main reason is that the spatial coherence of the laser fluctuates temporally and spatially, but the average photon scattering rate varies little, which makes the total number of atoms and the atomic density distribution unchanged.     

A STUDY ON ABSORPTION OF Na ATOMS ON Si(100) 2×1 SURFACES WITH DV-Xα METHOD

The Na absorption on Si(100) 2×1 surface is studied with quantum chemistry molecular cluster method. The calculated results show that the most favourable absorption site of Na is the cave site and the charge transfer of Na atom to Si is large when the Na coverage is smaller than 0.5 monolayer (ML). A Na chain is formed along the cave sites at the 0.5 ML Na coverage, the charge transfer then becomes small. The calculated density of states show that the Na atoms are metallic along the chain. At 1 ML coverage, the Na atoms occupy both the cave and pedestal sites and form a double-layer. There is a charge transfer of 0.5e from each Na atom to the Si surface. The calculated surface energy shows that the saturation absorption of Na on Si surface is 1 ML.     

Teleportation of N-qubit W State without Bell-State Measurement via Selective Resonant Interaction in Cavity QED

We present a scheme in which the N-atom W state is teleported by employing the selective interaction of a cavity field with a driven three-level atom in the A configuration and detecting a single atom in one of the ground states. The long-lived W state is teleported from atom A to atom B when the atoms B and A are sent through a cavity successively and atom A is then detected. The advantage is that the present one does not involve the Bell-state measurement and is robust against the atomic spontaneous emission.     

Ab Initio Calculation of Vacancies and Interstitials in NiSi2

An ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximations has been utilized to investigate the electronic structure, atomic geometry, formation energy to provide a better understanding of properties of Ni disilicide. The vacancy and interstitial formation energies largely depend on the atomic chemical potentials. The formation energies of vacancies Vsi and VNi are in the range of 0.04-0.56 eV and 1.25-2.3eV, respectively and the formation energies of Si and Ni interstitials are 3.89-4.42eV and 0.67-1.71 eV,respectively. The smaller Ni interstitial formation energy is in agreement with the experimental result that Ni interstitial atom is dominant diffusion species in NiSi2.     

First-principles calculations for titanium monoxide clusters TinO （n=1-9）

Based on the density-functional theory, this paper studies the geometric and magnetic properties of TinO （n=1-9） clusters. The resulting geometries show that the oxygen atom remains on the surface of clusters and does not change the geometry of Tin significantly. The binding energy, second-order energy differences with the size of clusters show that Ti7O cluster is endowed with special stability. The stability of TinO clusters is validated by the recent time-of-flight mass spectra. The total magnetic moments for TinO clusters with n=1-4, 8-9 are constant with 2 and drop to zero at n=5-7. The local magnetic moment and charge partition of each atom, and the density of states are discussed. The magnetic moment of the TinO is clearly dominated by the localized 3d electrons of Ti atoms while the oxygen atom contributes a very small amount of spin in TinO clusters.     

Quantum simulation for peak broadening in atom lithography

A grating structure with period of half of the laser wavelength generated by focusing Cr atoms with nearly resonant laser standing wave atom lens was simulated using a quantum-mechanical model.The influence of thermal atomic source on atom focusing,including the statistical distribution of the longitudinal veloc- ity and the beam divergence,was discussed.The background and full-width at half-maximum (FWHM) of atomic density peaks with v_z in Maxwell distribution and v_(x0) in Gaussian distribution increase sig- nificantly compared with ideal atoms.Collimating atoms with laser cooling is necessary to decrease the peak broadening.     

Probing structural and electronic properties of divalent metal Mgn+1 and SrMgn (n=2–12) clusters and their anions

Divalent metal clusters have received great attention due to the interesting size-induced nonmetal-to-metal transition and fascinating properties dependent on cluster size,shape,and doping.In this work,the combination of the CALYPSO code and density functional theory(DFT)optimization is employed to explore the structural properties of neutral and anionic Mg_n+1 and SrMgn(n=2-12)clusters.The results exhibit that as the atomic number of Mg increases,Sr atoms are more likely to replace Mg atoms located in the skeleton convex cap.By analyzing the binding energy,second-order energy difference and the charge transfer,it can be found the SrMg9 cluster with tower framework presents outstanding stability in a studied size range.Further,bonding characteristic analysis reveals that the stability of SrMg9 can be improved due to the strong s-p interaction among the atomic orbitals of Sr and Mg atoms.     

Density functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin （n - 1-8） clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital （NBO） are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6 clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.