•Phase transition and thermodynamic properties of cubic ZnN are reported.•The pressure up to 150 GPa.•The temperature up to 2000 K.In the current work, the aim is to report systematic results from first-principles calculations with density functional theory (DFT) on three cubic structures, rock salt (NaCl-type), zinc blende (ZnS-type), and cesium chloride (CsCl-type), of ZnN under high pressure. From the enthalpy versus pressure relations, we find that the NaCl-type phase of ZnN is more stable than the ZnS-type phase when the pressure higher than 2.55 GPa and high-pressure NaCl-type phase will stabilize up to 150 GPa. Through the careful evaluation with the quasi-harmonic Debye model, a complete set of thermodynamic data up to 2000 K, including PVT equation of state, isothermal bulk modulus, Debye temperature, Grüneisen parameter, thermal expansivity, heat capacity, and entropy for the ZnN with high-pressure NaCl-type structure is achieved. This set of data is considered as the useful information to understand the high-temperature and high-pressure properties of ZnN.

Molecular dynamic (MD) simulation has been performed to investigate the physical properties of ThO2 in the temperature range 300–3000 K. Using the three-point method, the parameters of Born–Mayer–Huggins potential with partially ionic model are obtained by fitting the lattice constants with experimental values. We predict that the melting point of ThO2 is 3650 ± 10 K. Besides, the lattice parameter, linear thermal expansion coefficient and thermal conductivity of ThO2 are systematically evaluated in high temperature range. In order to validate the potential for description of the ThO2, it has been used to predict specific heat, bulk modulus and defect energy which are in good agreement with previous values. We further calculate the lattice parameters, thermal expansion and thermal conductivity of Th1−yUyO2 and Th1−yPuyO2. The calculated lattice parameters of mixed fuels closely follow the Vegard’s law. With the improvement of the content y of doped U and Pu, thermal expansion coefficients both of them increase while the thermal conductivities decrease. The influence of Pu is more significant than U for thermal properties of ThO2.

Physical properties of mixed-oxide fuel (U0.75Pu0.25)O2−x (x=0.0,0.02,0.06,0.1,0.15,0.2,0.25) have been investigated by the molecular dynamic (MD) simulation in the temperature range 300–3000 K. The lattice parameter, linear thermal expansion coefficient, compressibility, bulk modulus and thermal conductivity are systematically investigated and analyzed by comparison with experiments and previous calculations. The calculated results of physical property are in good agreement with the experimental values and literature data. The oxygen vacancies have a significant effect on thermal properties of MOX. As oxygen vacancies increase, the bulk modulus gradually tend to be linear relationship with temperature and the thermal conductivity decreases very clearly, also, the temperature dependence weakens. In addition, we found that the influence of plutonium concentration for thermal conductivity is so small that it can be ignored when oxygen vacancies are existent.

Equilibrium geometries of AlnTi (n = 2–24) clusters were studied using density-functional theory with generalized gradient approximation. The resulting geometries showed that the titanium atom remains on the surface of clusters for n < 20 but is endohedrally doped from n = 20. This structural transition confirms the previous experiment results obtained by studying their abilities for argon physisorption (Lang, S. M.; Claes, P.; Neukermans, S.; Janssens, E. J. Am. Soc. Mass Spectrom.2011, 22, 1508). The average bond lengths, coordination numbers, relative stabilities, electronic properties, and other relevant properties were discussed. It was found that the doped titanium atoms strengthen the stabilities of the pure aluminum clusters. The coordination numbers of titanium atoms along with the average Al–Ti bond lengths undergo dramatic increases during the structural transition. The intra-atomic hybridization exists in both Ti and Al atoms, and charge transfer from Al atoms to Ti atom were found in these complexes, which should reflect the strength of Al–Ti interactions. Electronic structure analysis based on the partial density of states reveals stronger Al–Ti interactions for the endohedrally doped structures.

The X-ray emission spectra of nickel plasma were simulated under the collisional radiative model (CRM) by using the flexible atomic code (FAC). The dynamical processes including collisional excitation (CE), radiative recombination (RR), dielectronic recombination (DR), collisional ionization (CI) and resonance excitation were considered in the model, and the rate coefficients of DR, RR as well as CI were consistent with previous results within 15%. It was found that the contributions to spectra from cascades and indirect processes could not be ignored. The intensities of spectral lines for lithium-like nickel L-shell ions are sensitive to the electron temperature. The good agreement between present spectral peaks and earlier observed results can be taken as a measure of the accuracy of the present work.Highlights► DR, RR and CI were consistent with the previous results within 15%. ► Cascades and indirect processes could not be ignored in simulation. ► The spectral intensities were sensitive to the electron temperature. ► Present spectra were agreeing with the previous experiments and the results in NIST.

Equilibrium geometric structures of coinage-metal aluminum compounds AgnAl(0,+1) (n = 1–7) are first predicted by density-functional theory calculations with relativistic pseudopotentials. The stability of the ground state structures of these clusters is examined via the analysis of the binding energies (BE) and second difference energy. In addition, adiabatic ionization potential (AIP), energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, possible dissociation channels are also presented and discussed. Remarkable odd–even alternation behaviors have been observed. The results show that n = 6 is the magic number for AgnAl+, and n = 5 is predicted as the magic number for AgnAl. Moreover, for neutral clusters, doping clusters are more stable than the corresponding pure clusters.

A density functional method BPBE with pseudo-potential basis set CEP-121G is selected from different DFT methods to study Tin (n = 2–5) clusters. The stable geometries with different spins are determined. Ti dimer has a ground 3Δg state with bond length of 1.943 Å. The ground state structure of Ti trimer is an isosceles triangle (C2v). For Ti tetramer and pentamer, the ground state structures are distorted tetrahedron (D2d) and triangular bipyramid (C2v), respectively. For the ground states of Ti2−5 clusters, the natural bond orbital analysis is performed, and then we find the distribution of the unpaired electrons. Our results also show that the 4s orbital hybridizes with the 3d orbital. For the ground states, the vibrational spectra are gotten and the vibrational modes corresponding to the maximal IR peaks are determined.

Based on the relativistic effective core potential (RECP/SDD) for Pd atom and AUG-cc-pVTZ basis function for N atom, the structures of PdN and PdN2 have been optimized using B3LYP method. The results show that the ground state of PdN is 4Σ− and the ground state of PdN2is C∞V symmetry and 1Σ+ state. The Murrell-Sorbie potential energy function of PdN molecule has been fitted through the least square fitting, and the potential energy function of PdN2is based on many-body expansion theory. The potential energy curves describe the structure character of PdN and PdN2 ground state molecules correctly, and detail the inner transfer process of Pd. There is a saddle point in C2V structure (RNN= 0.11700 nm, RPdN= 0.22088 nm). The energy barrier of inner transfer is 0.5197 eV, which is close to the calculated value 0.4560 eV