On chemical bonding of Helium with hcp-Beryllium

Pre-melting hcp to bcc Transition in Beryllium

Beryllium (Be) is an important material with wide applications ranging from aerospace components to X-ray equipments. Yet a precise understanding of its phase diagram remains elusive. We have investigated the phase stability of Be using a recently developed hybrid free energy computation method that accounts for anharmonic effects by invoking phonon quasiparticles. We find that the hcp to bcc transition occurs near the melting curve at 0<P<11 GPa with a positive Clapeyron slope of 41 K/GPa. The bcc phase exists in a narrow temperature range that shrinks with increasing pressure, explaining the…

基于从头算准谐自由能计算的hcp金属高温高压热弹性：以铍为例

High temperature and pressure thermoelasticity of hcp metals from ab initio quasi-harmonic free energy calculations: the beryllium case

该研究以hcp结构铍为例，在准谐近似下开展从头算热弹性研究，量化了零静态内应力近似的精度，对比了多种近似方法的差异，为极端条件下hcp金属热弹性研究提供实用方法。

Beyond chemical accuracy: The pseudopotential approximation in diffusion Monte Carlo calculations of the HCP to BCC phase transition in beryllium

Motivated by the disagreement between recent diffusion Monte Carlo calculations and experiments on the phase transition pressure between the ambient and beta-Sn phases of silicon, we present a study of the HCP to BCC phase transition in beryllium. This lighter element provides an oppor- tunity for directly testing many of the approximations required for calculations on silicon and may suggest a path towards increasing the practical accuracy of diffusion Monte Carlo calculations of solids in general. We demonstrate that the single largest approximation in these calculations is the pseudopotenti…

High Pressure Phase Diagram of Beryllium from \emph{Ab Initio} Free Energy Calculations

We use first principles molecular dynamics simulations coupled to the thermodynamic integration method to study the hcp-bcc transition and melting of beryllium up to a pressure of 1600~GPa. We derive the melting line by equating solid and liquid Gibbs free energies, and represent it by a Simon Glatzel fit $T_m= 1564~\text{K} (1 + P/(15.6032 ~\text{GPa}))^{0.383}$, which is in good agreement with previous two-phase simulations below 6000~K. We also derive the hcp-bcc solid-solid phase boundary and show the quasiharmonic approximation underestimates the stability of the hcp structure, predicting…

Structure, elastic and bonding properties of hcp ZrxTi1-x binary alloy from first-principles calculations

First principles calculations were performed to study the structural, elastic, and bonding properties of hcp ZrxTi1-x binary alloy. The special quasi- random structure (SQS) method is employed to mimic the random hcp ZrxTi1-x alloy. It is found that Bulk modulus, B, Young's modulus, E, and shear modulus, G, exhibit decreasing trends as increasing the amount of Zr. A ductile behavior ZrxTi1-x is predicted in the whole composition range. In terms of Mulliken charge analisis, we found that the element Ti behaves much more electronegative than Zr in hcp ZrxTi1-x alloy, and the charge transfer of a…

Quantum chemical studies on beryllium hydride oligomers

The present study explores electronic and structural properties, ionization potential (IP), electron affinity (EA), polarizability (α), chemical potential (μ), hardness (η), softness (S), band gap (ΔE(HOMO-LUMO)) and spectral characteristics of beryllium hydride oligomers by quantum chemical treatment. The discrepancies in the calculated reactive descriptors of molecules are presumably due to variations in electron distribution and spin pairing near Fermi level. The molecules BeH2, Be3H5, Be5H10, Be7H14 and Be9H18 have been found to be more stable than Be2H4, Be4H8, Be6H12, Be8H16 and Be10H20.…