Projects per year
Abstract
It is shown that the enthalpy of any close packed structure for a given element can be characterized as a linear expansion in a set of continuous variables alpha(n), which describe the stacking configuration. This enables us to represent the infinite, discrete set of stacking sequences within a finite, continuous space of the expansion parameters Hn. These Hn determine the stable structure and vary continuously in the thermodynamic space of pressure, temperature, or composition. The continuity of both spaces means that only transformations between stable structures adjacent in the Hn space are possible, giving the model predictive as well as descriptive ability. We calculate the Hn using density functional theory (DFT) and interatomic potentials for a range of materials. Some striking results are found: e.g., the LennardJones potential model has 11 possible stable structures and over 50 phase transitions as a function of cutoff range. The very different phase diagrams of Sc, Tl, Y, and the lanthanides are understood within a single theory. We find that the widely reported 9Rfcc transition is not allowed in equilibrium thermodynamics, and in cases where it has been reported in experiments (Li, Na), we show that DFT theory is also unable to predict it.
Original language  English 

Article number  205701 
Number of pages  5 
Journal  Physical Review Letters 
Volume  119 
Issue number  20 
Early online date  14 Nov 2017 
DOIs  
Publication status  Published  17 Nov 2017 
Keywords
 INTERATOMIC POTENTIALS
 ISINGMODEL
 POLYTYPISM
 PRESSURE
 METALS
 SEQUENCE
 YTTRIUM
 4F
Projects


Interatomic potentials for oxide  metal interfaces in molecular dynamics
1/05/14 → 30/04/19
Project: Research
Profiles

Graeme Ackland
 School of Physics and Astronomy  Chair in Computer Simulation
Person: Academic: Research Active