ABINIT Discussion Forums

Hello,

An abinit script about one Cu cell gives me invariably Etotal near -194 Ha.
After some researches it appears that Etotal is roughly -60Ha.
I have modified powercutdg, ecut, Psp, nband, occopt, tsmear, kptrlat etc ... and SCF does function (correct convergence)
Excepting an eventual core contribution not included, now, the only false parameter to my sense could be the cell geometry.
I am inclined to it beceause when I try a loop on distance acell, it does not show a minimum.

However I have taken the cell distances on litterature.
An example script is below :

#Specific to ground state calculation
tolvrs 1.0d-18 # SCF stopping criterion

#Definition of occupation numbers
occopt 4 #voir tbase4_1.in et changer eventuellement le modele de smearing
tsmear 0.05

#######################################################################
#Common input variables

#Definition of the unit cell
acell 3*11.78 # This is equivalent to 11.78 11.78 11.78, mesh = 6,23Angstrom = 11.78 Bohr
rprim 0.0 0.5 0.5 # In lessons 1 and 2, these primitive vectors
0.5 0.0 0.5 # (to be scaled by acell) were 1 0 0 0 1 0 0 0 1
0.5 0.5 0.0 # that is, the default.

#Definition of the atom types
ntypat 1 # There are one type of atom
znucl 29 # The keyword "znucl" refers to the atomic number of the
# possible type(s) of atom. The pseudopotential(s)
# mentioned in the "files" file must correspond
# to the type(s) of atom. Here, type 1 is Copper


#Definition of the atoms
natom 1 # There are one atom
typat 1 # it is of type 1 (Cu).
xred # This keyword indicate that the location of the atoms
# will follow, one triplet of number for each atom
0.0 0.0 0.0 # Triplet giving the REDUCED coordinate of atom 1.


#Gives the number of band, explicitely (do not take the default)
#nband 8 # For an insulator (if described correctly as an insulator
# by DFT), there is no need to include conduction bands
# in response-function calculations pas de nband pour les metaux mais occopt 4,5...

#Exchange-correlation functional
ixc 7 # - LDA conviendrait pour copper - la valeur 7 est compatible avec le pseudopote

#Definition of the planewave basis set
ecut 10.0 # Maximal kinetic energy cut-off, in Hartree
pawecutdg 20.0 # Must be larger than ecut fot double FFT grid

#Definition of the k-point grid
kptrlatt -4 4 4 # In cartesian coordinates, this grid is simple cubic, and
4 -4 4 # actually corresponds to the so-called 8x8x8 Monkhorst-Pack grid.
4 4 -4 # It might as well be obtained through the use of
# ngkpt, nshiftk and shiftk .

#Definition of the SCF procedure
nstep 15 # Maximal number of SCF cycles
diemac 1.0d+6 # Although this is not mandatory, it is worth to
# precondition the SCF cycle. The model dielectric
# function used as the standard preconditioner
# is described in the "dielng" input variable section
# The dielectric constant of Copper is chosen infinite or very high

## After modifying the following section, one might need to regenerate the pickle database with runtests.py -r
#%%<BEGIN TEST_INFO>
#%% [setup]
#%% executable = abinit
#%% test_chain = copper1_1.in
#%% [files]
#%% files_to_test =
#%% trf1_1.out, tolnlines= 0, tolabs= 0.000e+00, tolrel= 0.000e+00
#%% psp_files = Cu_LDA_abinit
#%% [paral_info]
#%% max_nprocs = 2
#%% [extra_info]
#%% authors = Unknown
#%% keywords =
#%% description = Crystalline Copper : computation of the total energy
#%%<END TEST_INFO>

\end{verbatim}

Could you correct me if I made a big error ???
Sorry to post about elementary thing,
JLuc

fcc copper has a lattice constant of about 3.61 angstrom, your value corresponds to about twice that. It almost looks like you got the lattice constant from somewhere in Bohr, but thought it was in angstrom and then converted the number to Bohr. Short answer is that your acell is much larger than the physical value for this system.

best wishes,

Joe

Thank you Joe,

1) trivial error : today I have progressed...
Don't remember why I have put 11.78. There were first trials long ago. The correct anwer is acell 6.84 (6.84 Bohr = 3.6/0.529) and rprim = 0.5 M where M is the matrix of primitive cell I have already written. Also I must not include any correction inside acell, as probably I did.
With that prerequisites, I did a little scan between acell 6.44 and acell 7.34, noting Etotal. I notice a parabola with a minimum at -197,4581...Ha, which happens for acell 6.64. (I give here only 4 characteristic digits). Of course, it is possible to refine, these results are not precise, but it seems that near that given distance, we observe an electronic minimum. So I hope I should be on the right way for next steps.

2) now that I have corrected the elementary faults, it remains that Etotal concept is not so clear for me. How to add the ''constant'', in order to obtain ''real'' total energy, knowing that for copper for exemple, it is something like -70Ha, ie -1638,...eV ?

Will some additional tools or methods give me these figures, or is it a vain tentative, as abinit claims that Total Energy is defined relatively ? In publications, like
''Converged properties of clean metal surfaces by all-electron first-principles calculations'', Juarez L.F. Da Silva a, and al, from Surface Science 600 (2006) 703–715
They deal with cohesive energy, so Etotal in the global sense, may be interesting. Additionnally I may link Etotal with work function, and not only for copper, so that matter could concern me.
So may I let that point 2) open ?...

Best wishes
JLuc

Hello,

In that post for GS of bulk copper, I raised 2 questions :

1- pertinence of data in my input file and consequences on calculations,
2- meaning of Etotal

I consider that Josef W. Zwanziger did really help me on 1; with the correct cell, I re computed energies, WFs, bands, ... Nevertheless It remains that Etotal =-197,... Ha, a considerable figure which is modified by ion-ion interaction -and other terms- to give -70 Ha approximately. Note that all the 11 bands were included in calculation.

Regarding 2) it may be an other topic and I propose to ''take my time to learn'' and report that discussion.

So I estimate that post as SOLVED.