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The ensemble-DFT (eDFT) is a robust method to simulate the metals in the framework of ''ab-initio'' molecular dynamics. It was introduced in 1997 by Marzari et al.
The specific subroutines for the eDFT are in ensemble_dft.f90 where you
define all the quantities of interest. The subroutine inner_loop_cold.f90
called by cg_sub.f90, control the inner loop, and so the minimization of
the free energy A
To select a eDFT calculations, the user has to choice:
The input for an Al surface is:
All the other parameters have the same meaning in the usual CP input,
and they are discussed above.
calculation = 'cp'
occupations= 'ensemble'
tcg = .true.
passop= 0.3
maxiter = 250
to use the CG procedure. In the eDFT it is also the outer loop, where thei
energy is minimized with respect to the wavefunction keeping fixed the
occupation matrix. While the specific parameters for the inner loop.
Since eDFT was born to treat metals, keep in mind that we want to describe
the broadening of the occupations around the Fermi energy.
Below the new parameters in the electrons list, are listed.
NOTE: degauss is in Hartree, while in PWscf is in Ry (!!!).
The tyPical range is 0.01-0.02 Ha.
&CONTROL
calculation = 'cp',
restart_mode = 'from_scratch',
nstep = 10,
iprint = 5,
isave = 5,
dt = 125.0d0,
prefix = 'Aluminum_surface',
pseudo_dir = '~/UPF/',
outdir = '/scratch/'
ndr=50
ndw=51
/
&SYSTEM
ibrav= 14,
celldm(1)= 21.694d0, celldm(2)= 1.00D0, celldm(3)= 2.121D0,
celldm(4)= 0.0d0, celldm(5)= 0.0d0, celldm(6)= 0.0d0,
nat= 96,
ntyp= 1,
nspin=1,
ecutwfc= 15,
nbnd=160,
nelec=291,
xc_type = 'pbe'
occupations= 'ensemble',
smearing='cs',
degauss=0.018,
/
&ELECTRONS
orthogonalization = 'Gram-Schmidt',
startingwfc = 'random',
ampre = 0.02,
tcg = .true.,
passop= 0.3,
maxiter = 250,
emass_cutoff = 3.00,
conv_thr=1.d-6
n_inner = 2,
lambda_cold = 0.03,
niter_cold_restart = 2,
/
&IONS
ion_dynamics = 'verlet',
ion_temperature = 'nose'
fnosep = 4.0d0,
tempw = 500.d0
/
ATOMIC_SPECIES
Al 26.89 Al.pbe.UPF
NOTA1 remember that the time step is to integrate the ionic dynamics,
so you can choose something in the range of 1-5 fs.
NOTA2 with eDFT you are simulating metals or systems for which the
occupation number is also fractional, so the number of band, nbnd, has to
be chosen such as to have some empty states. As a rule of thumb, start
with an initial occupation number of about 1.6-1.8 (the more bands you
considera, the more the calculation is accurate, but it also takes longer.
The CPU time scales almost linearly with the number of bands.)
NOTA3 the parameter emass_cutoff is used during the preconditioning
and it has a completely different meaning with respect to plain CP.
It ranges between 4 and 7.
Next: 5.6 About nr1b, nr2b,
Up: 5 Using CP
Previous: 5.4 Variable-cell MD
Contents
Paolo Giannozzi
2010-04-08