A simple equation of state (EOS) in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter co...A simple equation of state (EOS) in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter cold energy expression to represent the static EOS term, which can correctly produce cohesive energy without any spurious oscillations in the extreme compression and expansion regions, We developed a Pade approximation-based analytic Debye quasiharmonic model with high accuracy which improves the performance of EOS in the low temperature region. The anharmonic effect is taken into account by using a semi-empirical approach. Its reasonability is verified by the fact that the total thermal pressure tends to the lowest-order anharmonic expansion in the literature at low temperature, and tends to ideal-gas limitation at high temperature, which is physically correct. Besides, based on this approach, the anharmonic thermal pressure can be expressed in the Griineisen form, which is convenient for applications. The proposed EOS is used to study the thermodynamic properties of MgO including static and shock compression conditions, and the results are very satisfactory as compared with the experimental data.展开更多
A five-parameter equation of state (EOS) is proposed to correctly incorporate the cohesive energy data in it without physically incorrect oscillations. The proposed EOS is applied to 10 selected metals. It is shown ...A five-parameter equation of state (EOS) is proposed to correctly incorporate the cohesive energy data in it without physically incorrect oscillations. The proposed EOS is applied to 10 selected metals. It is shown that the calculated compression curves are in good accordance with the experimental data. The values of the bulk modulus and its derivative with respect to pressure extracted from the proposed EOS remain almost unchanged while the data range used is varied.展开更多
The electronic structures of pure Ti, Zr and Hf metals with hcp structure were determined by one atom (OA) theory. According to the electronic structures of these metals,their potential curves, cohesive energies, latt...The electronic structures of pure Ti, Zr and Hf metals with hcp structure were determined by one atom (OA) theory. According to the electronic structures of these metals,their potential curves, cohesive energies, lattice constants, elasticities and the temperature dependence of linear thermal expansion coefficients were calculated. The electronic structures and characteristic properties of these metals with bcc and fcc structures and liquids were also studied. The results show that the electronic structures of Ti, Zr and Hf metals are respectively [Ar](3d n) 0.481 0 (3d c) 2.085 7 (4s c) 1.000 0 (4s f) 0.433 3 , [Kr](4d n) 0.396 8 (4d c) 2.142 8 (5s c) 1.262 0 (5s f) 0.198 4 , [Xe](5d n) 0.368 0 (5d c) 2.041 4 (6s c) 1.406 6 (6s f) 0.184 0 . It is explained why the pure Ti, Zr and Hf metals with hcp and bcc structures can exist naturally, while those with fcc structure can not.展开更多
Using the new developed valence bond theory of metals,the electronic structure,crystal structure and physical properties of Au metal have been systematically analysed.It has been determined that its electronic structu...Using the new developed valence bond theory of metals,the electronic structure,crystal structure and physical properties of Au metal have been systematically analysed.It has been determined that its electronic structure is(5d_(n))^(4.65)(5d_(c))^(4.71)(6s_(c))^(0.62)(6s_(f))^(1.02).According to this electronic structure,lattice constant,cohesive energy.potential curve,bulk modulus and temperature dependence of liner thermal expansion coeCHcient have been calculated.The theoretical values of properties are all in good agreement with experimental results.This electronic structure has been verified in part by linear rigorous cellular method of band theory.It shows that the valence bond theory has been reached perfectly.展开更多
The electronic structure, cohesive energy and interfacial energy of ferrite(100)/NbC(100) and TiC(100)/NbC(100) interfaces have been investigated by the first-principles calculation. Moreover, the heterogeneou...The electronic structure, cohesive energy and interfacial energy of ferrite(100)/NbC(100) and TiC(100)/NbC(100) interfaces have been investigated by the first-principles calculation. Moreover, the heterogeneous nuclei mechanism of NbC particle was also analyzed. The results showed that the stacking sequences have a great influence on the cohesive energy and equilibrium interfacial separation of the abovementioned interfaces. Compared with C-terminated interfaces, the cohesive energy of Nb-terminated ones is lower while the equilibrium interface distance is larger. Among the two C-terminated interface structures, the interfacial energy between the NbC and ferrite is 4.54 J/m^2, which is larger than that of NbC/TiC interface(1.80 J/m^2). Therefore, NbC particles prefer heterogeneous nucleation on TiC particles surface rather than the ferrite matrix, which agrees well with the experimental result.展开更多
INTRODUCTIONIn the deyelopment of material science,it 15 desirable that theand elastic eonstants whieh are the imPoaceurately calculated by means ofrtant meehanical ProPertieseohesive energiesof erystals ean bePhysiea...INTRODUCTIONIn the deyelopment of material science,it 15 desirable that theand elastic eonstants whieh are the imPoaceurately calculated by means ofrtant meehanical ProPertieseohesive energiesof erystals ean bePhysieal meehanies method .展开更多
The conformation, the chain packing stabilization and the unit cell modeling of poly(p-phenylene benzobisthiazole) have been investigated by using molecular simulation techniquein the present work. A coupling behaviou...The conformation, the chain packing stabilization and the unit cell modeling of poly(p-phenylene benzobisthiazole) have been investigated by using molecular simulation techniquein the present work. A coupling behaviour of σ-bond rotations at either side of the pheny-lene ring or the heterocyclic ring was found surely to exceed a length of the repeat unit ofthe polymer chain. For a single chain model, the stable torsion angle of the repeat resultedat 14°. In the crystalline cell minimization, the dihedral angle along the polymer chaincould even be stabilized in various values. It therefore indicates that the intermolecularinteraction does play a considerable role for this polymer forming the conformation. Ac-cording to cohesive energies calculated for these unit cell models, the torsion angle in themost stable crystalline cell is 0°. When the chains packing together, there exist so manyenergy stable wells along the chain axis 0.35--0.36nm apart from neighbouring chains.Most of the unit cells have quite closed cohesive energies. These factors thus cause thedifficulty of forming an unique perfect crystalline structure of the polymer. The presentstudy suggested a number of reasonable unit cells, and the most stable crystalline structurefor this polymer that is monoclinic, non-primitive unit cell.展开更多
Abrasive wear characteristics of polyethylene, polystyrene,polymethylmethacrylate, nylon 1010 and polyvinyl chloride were investigated. The volume relativewear resistance coefficients of these thermoplastic polymers a...Abrasive wear characteristics of polyethylene, polystyrene,polymethylmethacrylate, nylon 1010 and polyvinyl chloride were investigated. The volume relativewear resistance coefficients of these thermoplastic polymers are 18%-35% (hardened and lowtemperature tempered steel 45 was used as a comparing material), and have a linear correlation withsquare roots of their cohesive energy densities. The coefficients of linear correlation is 0.949.Wear morphologies were observed by scanning electron microscope (SEM). Main wear mechanism of thethermoplastic polymers includes brittle breaking for the hard and brittle polymers & plowing andfatiguing for the soft and tough ones.展开更多
According to the correlativity between energy, volume and electronic structure of characteristic crystals and bound conditions of OA theory, the Gibbs energy function, atomic volume function and electronic structure o...According to the correlativity between energy, volume and electronic structure of characteristic crystals and bound conditions of OA theory, the Gibbs energy function, atomic volume function and electronic structure of Ag Cu alloys have been determined. Then the electronic structure and properties of disordered alloys with any composition and ordered alloys with any ordering degree can be calculated. The number of d c covalent electrons in the states of Ag characteristic atoms decreases with the increase of Cu atoms in the nearest neighbouring shell. The number of d c covalent electrons in the states of Cu characteristic atoms decreases with the increase of Ag atoms in the nearest neighbouring shell. Such changes lead to the tendencies of atomic segregation and partition into two phases in the Ag Cu system.展开更多
Various silicon crystal structures with different atomic arrangements from that of diamond have been observed in chemically synthesized nanowires.The structures are typified by mixed stacking mismatches of closely pac...Various silicon crystal structures with different atomic arrangements from that of diamond have been observed in chemically synthesized nanowires.The structures are typified by mixed stacking mismatches of closely packed Si dimers.Instead of viewing them as defects,we define the concept of hexagonality and describe these structures as Si polymorphs.The small transverse dimensions of a nanowire make this approach meaningful.Unique among the polymorphs are cubic symmetry diamond and hexagonal symmetry wurtzite structures.Electron diffraction studies conducted with Au as an internal reference unambiguously confirm the existence of the hexagonal symmetry Si nanowires.Cohesive energy calculations suggest that the wurtzite polymorph is the least stable and the diamond polymorph is the most stable.Cohesive energies of intermediate polymorphs follow a linear trend with respect to their structural hexagonality.We identify the driving force in the polymorph formations as the growth kinetics.Fast longitudinal elongation during the growth freezes stacking mismatches and thus leads to a variety of Si polymorphs.The results are expected to shed new light on the importance of growth kinetics in nanomaterial syntheses and may open up ways to produce structures that are uncommon in bulk materials.展开更多
Although sulfide electrode materials in lithium battery systems have been intensively investigated due to their low-cost, high theoretical specific capacity, and energy density, there are few studies fousing on the ad...Although sulfide electrode materials in lithium battery systems have been intensively investigated due to their low-cost, high theoretical specific capacity, and energy density, there are few studies fousing on the adhesion properties, including the physical origin of hetero-coordination resolved interface relaxation, binding energy and the energetic behavior, and even the accurate quantitative information. In this paper, we present an approach for quantifying the interface adhesion properties of sulfide electrode materials resolved by the combination of bond order-length-strength theory(BOLS) and X-ray photoelectron spectroscopy(XPS), which has enabled clarification of the interface adhesion nature. The results show that the Cu 2p, Fe 2p, and S 2p electrons of Cu S and FeS_(2) compounds shift negatively due to the charge polarization of the conduction electrons of the heteroatoms, while Mo 3d, Sn 3d electrons of Mo S2 and Sn S2 and the C 1 s and S 2p electrons of CS compound shift positively due to the quantum trapping. It is noted that the exact interface adhesion energies of Cu S is 3.42 J m^(-2), which is consistent with the calculation result. The approach can not only clarify the origin of the interface adhesion properties of sulfide electrode materials,but also derive their quantification information from atomistic sites.展开更多
基金Project supported by the Joint Fund of National Natural Science Foundation of China and China Academy of Engineering Physics(Grant No. 10876008)
文摘A simple equation of state (EOS) in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter cold energy expression to represent the static EOS term, which can correctly produce cohesive energy without any spurious oscillations in the extreme compression and expansion regions, We developed a Pade approximation-based analytic Debye quasiharmonic model with high accuracy which improves the performance of EOS in the low temperature region. The anharmonic effect is taken into account by using a semi-empirical approach. Its reasonability is verified by the fact that the total thermal pressure tends to the lowest-order anharmonic expansion in the literature at low temperature, and tends to ideal-gas limitation at high temperature, which is physically correct. Besides, based on this approach, the anharmonic thermal pressure can be expressed in the Griineisen form, which is convenient for applications. The proposed EOS is used to study the thermodynamic properties of MgO including static and shock compression conditions, and the results are very satisfactory as compared with the experimental data.
基金Project supported by the Joint Fund of National Natural Science Foundation of China and China Academy of Engineering Physics (Grant No.10876008)the New Century Excellent Researcher Award Program from the Educational Ministry of China(Grant No.NCET-05-0799)the Academic Excellence of University of Electronic Science and Technology of China (Grant No.23601008)
文摘A five-parameter equation of state (EOS) is proposed to correctly incorporate the cohesive energy data in it without physically incorrect oscillations. The proposed EOS is applied to 10 selected metals. It is shown that the calculated compression curves are in good accordance with the experimental data. The values of the bulk modulus and its derivative with respect to pressure extracted from the proposed EOS remain almost unchanged while the data range used is varied.
基金TheNaturalScienceFoundationofHunanProvince (No .99JZY10 0 5 )
文摘The electronic structures of pure Ti, Zr and Hf metals with hcp structure were determined by one atom (OA) theory. According to the electronic structures of these metals,their potential curves, cohesive energies, lattice constants, elasticities and the temperature dependence of linear thermal expansion coefficients were calculated. The electronic structures and characteristic properties of these metals with bcc and fcc structures and liquids were also studied. The results show that the electronic structures of Ti, Zr and Hf metals are respectively [Ar](3d n) 0.481 0 (3d c) 2.085 7 (4s c) 1.000 0 (4s f) 0.433 3 , [Kr](4d n) 0.396 8 (4d c) 2.142 8 (5s c) 1.262 0 (5s f) 0.198 4 , [Xe](5d n) 0.368 0 (5d c) 2.041 4 (6s c) 1.406 6 (6s f) 0.184 0 . It is explained why the pure Ti, Zr and Hf metals with hcp and bcc structures can exist naturally, while those with fcc structure can not.
基金supported by China National Nonferrous Metals Industry Corporation
文摘Using the new developed valence bond theory of metals,the electronic structure,crystal structure and physical properties of Au metal have been systematically analysed.It has been determined that its electronic structure is(5d_(n))^(4.65)(5d_(c))^(4.71)(6s_(c))^(0.62)(6s_(f))^(1.02).According to this electronic structure,lattice constant,cohesive energy.potential curve,bulk modulus and temperature dependence of liner thermal expansion coeCHcient have been calculated.The theoretical values of properties are all in good agreement with experimental results.This electronic structure has been verified in part by linear rigorous cellular method of band theory.It shows that the valence bond theory has been reached perfectly.
基金Funded by the National Natural Science Foundation of China(Nos.51174100,51564016 and 51564017)Natural Science Foundation of Jiangxi Province,China(No.20171ACB21042)
文摘The electronic structure, cohesive energy and interfacial energy of ferrite(100)/NbC(100) and TiC(100)/NbC(100) interfaces have been investigated by the first-principles calculation. Moreover, the heterogeneous nuclei mechanism of NbC particle was also analyzed. The results showed that the stacking sequences have a great influence on the cohesive energy and equilibrium interfacial separation of the abovementioned interfaces. Compared with C-terminated interfaces, the cohesive energy of Nb-terminated ones is lower while the equilibrium interface distance is larger. Among the two C-terminated interface structures, the interfacial energy between the NbC and ferrite is 4.54 J/m^2, which is larger than that of NbC/TiC interface(1.80 J/m^2). Therefore, NbC particles prefer heterogeneous nucleation on TiC particles surface rather than the ferrite matrix, which agrees well with the experimental result.
文摘INTRODUCTIONIn the deyelopment of material science,it 15 desirable that theand elastic eonstants whieh are the imPoaceurately calculated by means ofrtant meehanical ProPertieseohesive energiesof erystals ean bePhysieal meehanies method .
基金This project was supported by the National Basic Research Project-Macromolecular Condensed State, the National Natural Science Foundation of China and US-China Cooperative Research Program of NSF.
文摘The conformation, the chain packing stabilization and the unit cell modeling of poly(p-phenylene benzobisthiazole) have been investigated by using molecular simulation techniquein the present work. A coupling behaviour of σ-bond rotations at either side of the pheny-lene ring or the heterocyclic ring was found surely to exceed a length of the repeat unit ofthe polymer chain. For a single chain model, the stable torsion angle of the repeat resultedat 14°. In the crystalline cell minimization, the dihedral angle along the polymer chaincould even be stabilized in various values. It therefore indicates that the intermolecularinteraction does play a considerable role for this polymer forming the conformation. Ac-cording to cohesive energies calculated for these unit cell models, the torsion angle in themost stable crystalline cell is 0°. When the chains packing together, there exist so manyenergy stable wells along the chain axis 0.35--0.36nm apart from neighbouring chains.Most of the unit cells have quite closed cohesive energies. These factors thus cause thedifficulty of forming an unique perfect crystalline structure of the polymer. The presentstudy suggested a number of reasonable unit cells, and the most stable crystalline structurefor this polymer that is monoclinic, non-primitive unit cell.
文摘Abrasive wear characteristics of polyethylene, polystyrene,polymethylmethacrylate, nylon 1010 and polyvinyl chloride were investigated. The volume relativewear resistance coefficients of these thermoplastic polymers are 18%-35% (hardened and lowtemperature tempered steel 45 was used as a comparing material), and have a linear correlation withsquare roots of their cohesive energy densities. The coefficients of linear correlation is 0.949.Wear morphologies were observed by scanning electron microscope (SEM). Main wear mechanism of thethermoplastic polymers includes brittle breaking for the hard and brittle polymers & plowing andfatiguing for the soft and tough ones.
基金Project supported by the Na tional Natural Science Foundation of Chi m(Grant Nos.59371029,59671030
文摘According to the correlativity between energy, volume and electronic structure of characteristic crystals and bound conditions of OA theory, the Gibbs energy function, atomic volume function and electronic structure of Ag Cu alloys have been determined. Then the electronic structure and properties of disordered alloys with any composition and ordered alloys with any ordering degree can be calculated. The number of d c covalent electrons in the states of Ag characteristic atoms decreases with the increase of Cu atoms in the nearest neighbouring shell. The number of d c covalent electrons in the states of Cu characteristic atoms decreases with the increase of Ag atoms in the nearest neighbouring shell. Such changes lead to the tendencies of atomic segregation and partition into two phases in the Ag Cu system.
基金by a Department of Defense subcontract from Agiltron.Technical assistance from Y.Lin,Dr.D.Wang,Dr.J.Kong,and Y.-P.Hsieh is gratefully acknowledged.
文摘Various silicon crystal structures with different atomic arrangements from that of diamond have been observed in chemically synthesized nanowires.The structures are typified by mixed stacking mismatches of closely packed Si dimers.Instead of viewing them as defects,we define the concept of hexagonality and describe these structures as Si polymorphs.The small transverse dimensions of a nanowire make this approach meaningful.Unique among the polymorphs are cubic symmetry diamond and hexagonal symmetry wurtzite structures.Electron diffraction studies conducted with Au as an internal reference unambiguously confirm the existence of the hexagonal symmetry Si nanowires.Cohesive energy calculations suggest that the wurtzite polymorph is the least stable and the diamond polymorph is the most stable.Cohesive energies of intermediate polymorphs follow a linear trend with respect to their structural hexagonality.We identify the driving force in the polymorph formations as the growth kinetics.Fast longitudinal elongation during the growth freezes stacking mismatches and thus leads to a variety of Si polymorphs.The results are expected to shed new light on the importance of growth kinetics in nanomaterial syntheses and may open up ways to produce structures that are uncommon in bulk materials.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11972157 and 11872054)the Natural Science Foundation of Hunan Province (Grant Nos. 2020JJ2026 and 2021JJ30643)。
文摘Although sulfide electrode materials in lithium battery systems have been intensively investigated due to their low-cost, high theoretical specific capacity, and energy density, there are few studies fousing on the adhesion properties, including the physical origin of hetero-coordination resolved interface relaxation, binding energy and the energetic behavior, and even the accurate quantitative information. In this paper, we present an approach for quantifying the interface adhesion properties of sulfide electrode materials resolved by the combination of bond order-length-strength theory(BOLS) and X-ray photoelectron spectroscopy(XPS), which has enabled clarification of the interface adhesion nature. The results show that the Cu 2p, Fe 2p, and S 2p electrons of Cu S and FeS_(2) compounds shift negatively due to the charge polarization of the conduction electrons of the heteroatoms, while Mo 3d, Sn 3d electrons of Mo S2 and Sn S2 and the C 1 s and S 2p electrons of CS compound shift positively due to the quantum trapping. It is noted that the exact interface adhesion energies of Cu S is 3.42 J m^(-2), which is consistent with the calculation result. The approach can not only clarify the origin of the interface adhesion properties of sulfide electrode materials,but also derive their quantification information from atomistic sites.