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Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo calculations
 

Summary: Structural properties and enthalpy of formation of magnesium hydride
from quantum Monte Carlo calculations
M. Pozzo1
and D. Alfè1,2,3,*
1Department of Earth Sciences and Materials Simulation Laboratory, University College London, Gower Street,
London WC1E 6BT, United Kingdom
2Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
3London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
Received 8 November 2007; revised manuscript received 13 January 2008; published 7 March 2008
We have used diffusion Monte Carlo DMC calculations to study the structural properties of magnesium
hydride MgH2 , including the pressure-volume equation of state, the cohesive energy, and the enthalpy of
formation from magnesium bulk and hydrogen gas. The calculations employ pseudopotentials and B-spline
basis sets to expand the single particle orbitals used to construct the trial wave functions. Extensive tests on
system size, time step, and other sources of errors, performed on periodically repeated systems of up to 1050
atoms, show that all these errors together can be reduced to below 10 meV/f.u.. We find excellent agreement
with the experiments for the equilibrium volume of both the Mg and the MgH2 crystals. The cohesive energy
of the Mg crystal is found to be 1.51 1 eV and agrees perfectly with the experimental value of 1.51 eV. The
enthalpy of formation of MgH2 from Mg bulk and H2 gas is found to be 0.85 0.01 eV/f.u., or
82 1 kJ/mole, which is off the experimental one of 76.1 1 kJ/mole only by 6 kJ/mole. This shows that
DMC can almost achieve chemical accuracy 1 kcal/mole on this system. Density functional theory errors are

  

Source: Alfè, Dario - Departments of Earth Sciences & Physics and Astronomy, University College London

 

Collections: Physics; Geosciences