Phase stabilities first principle calculations

Mujica A and R J Needs 1993. First-principles Calculations of the Structural Properties, Stability, aind Band Structure of Complex Tetrahedral Phases of Germanium ST12 and BC8. Physical Review B48 17010-17017. 

A typical ab initio (first principles) calculation for lithium intercalation consists of two steps (i) energy calculation at 0 K to determine the ground states and relative energy difference between crystal structures and (ii) the construction and calculation of a free energy model to determine the phase stability at non-zero temperature. Dahn ef al. [37], Ceder ef al. [38] and Benco ef al. [41] all reported that the electrode potentials of transition metal oxides could be very well predicted by this method. In addition, Ceder ef al. constructed (on a theoretical basis) the phase diagram of IiCoO2 [40, 42,... 

Joseph Muscat, Varghese Swamy, Nicholas M. Harrison. First-principles calculations of the phase stability of Ti02. Physical Review B, 65, 2002 41. 

The field of first-principles calculations has matured over the past two decades to the point where these simulations are invaluable in guiding and interpreting experiments. While we will here focus on the thermodynamic quantities obtained using firsqtrinciples in order to study phase stability, a whole host of atomic and electronic structural properties can now be predicted with acceptable degrees of accuracy. Our goal in this chapter is to familiarize the reader with the basics of first-principles calculations (in particular density functional theory, abbreviated as DFT, and thermodynamic models that incorporate it) and show how these techniques have been applied to oxide systems in the literature. This chapter is outlined as follows ... 

Arroyo-DeDompablo ME, Van der Ven A, Ceder G (2002) First-principles calculations of lithium ordering and phase stability on Li Ni02. Phys Rev B 66 064112 1-9... 

Arroyo-DeDompablo ME, Ceder G (2003) First-principles calculations on LixNi02 phase stability and monoclinic distortion. J Power Sources 119121 654-657... 

In summary, we have demonstrated the possibility of calculating the phase stability of a magnetic random alloy from first principles by means of LMTO-CPA theory. Our calculated phase diagram is in good agreement with experiment and shows a transition from the partially ordered a phase to an hep random alloy at 85% Co concentration. 

Tinte et al.54 have carried out molecular dynamic simulations of first-principles based effective Hamiltonian for PSN under pressure and of PMN at ambient pressure that clearly exhibit a relaxor state in the paraelectric phase. Analysis of the short-to-medium range polar order allows them to locate Burns temperature Tb. Burns temperature is identified as the temperature below which dynamic nanoscale polar clusters form. Below TB, the relaxor state characterized by enhanced short-to-medium range polar order (PNR) pinned to nanoscale chemically ordered regions. The calculated temperature-pressure phase diagram of PSN demonstrates that the stability of the relaxor state depends on a delicate balance between the energetics that stabilize normal ferroelectricity and the average strength of quenched "random" local fields. 

Summarizing, first-principles theory is able quantitatively to describe the structural stabilities of new perovskite-like MFesN compounds, in particular the preference of the larger M atoms to go to the comer position, and ferromagnetic ground states result from an optimized chemical bonding due to the removal of formerly antibonding Fe-Fe states at the Fermi level. Due to the numerical accuracy of the pseudopotential GGA calculations, two unknown phases may be predicted as worthwhile synthetic goals. At ambient... 

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