[Pw_forum] LDA, PBE and PBEsol and Cohesive energy

[Elliot Menkah]

Hello everyone,
Problem 1
---------------------------------------
I'm computing for lattice constant and comparing the employment of
exchange correlation ultra-soft pp such as LDA, PBE and PBEsol. I know
LDA would underestimate the lattice parameter, PBE would overestimate it
but PBEsol should do better than PBE.

My calculations are shows LDA= 3.419  PBE= 3.516 PBEsol = 3.455 Angstom.
experimnetal value I'm comparing it to is 3.522 Ang

PBEsol gave a lower atomic lattice value than PBE.

What could be wrong with the composition of the system?

Attached is the input file(vc_ni-bulk-pbesol.in) for the PBEsol USPP
calculations.

Problem 2
-------------------------------------------
Trying to find Cohesive energy and I already have my energy of the bulk.
I'm now computing for the energy of a single atom in a vacuum system.

I added 15 15 15 Ang to the XYZ Cell parameters and the single atom sits
in a corner whiles I expect it to sit some where in the middle.

What I'm I not doing right please.

Attached is the respective (evac-ni.in) file too.
Thank you.




Kind Regards,



Elliot

-- 
Elliot S. Menkah
Research Student - Computational Chemistry/ Computational Material Science
Theoretical and Computational Chemistry
Dept. of Chemistry
Kwame Nkrumah UNiversity of Sci. and Tech.
Kumasi
Ghana

Tel: +233 243-055-717

Alt Email: elliotsmenkah at gmail.com
           elliotsmenkah at hotmail.com


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&CONTROL
	title = 'Bulk-Nickel',
	calculation = 'vc-relax',
 	restart_mode = 'from_scratch',
   	wf_collect = .true.,
	outdir = './temp',
	wfcdir = './wftemp',
	pseudo_dir = '/home/mmc14/pseudo',
       	prefix = 'Ni-bulk-pbe',
      	tstress = .true.,
      	tprnfor = .true.,
/
&SYSTEM
     	ibrav        = 0,
     	celldm(1)    = 1.889725989,
     	nat          = 4,
     	ntyp         = 1,
     	nbnd         = 30,
     	ecutwfc      = 40.0
     	ecutrho      = 320.0,
	occupations  ='smearing',
       	smearing     ='mp',
       	degauss      =0.005D0,
	nspin	     = 2,
       	starting_magnetization(1)=0.5,
/
&ELECTRONS
 	electron_maxstep = 100,
        conv_thr = 1.0D-8,
      	mixing_beta = 0.2
/
&IONS
     ion_dynamics = 'bfgs' ,
/
&CELL
               cell_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
	Ni1 58.6934   Ni.pbesol-n-kjpaw_psl.0.1.UPF
ATOMIC_POSITIONS {alat}
       Ni1       1.7691699470     1.7691699470     0.0000000000
       Ni1       0.0000000000     0.0000000000     0.0000000000
       Ni1       1.7691699470     0.0000000000     1.7691699470
       Ni1       0.0000000000     1.7691699470     1.7691699470
K_POINTS automatic
7 7 7   0 0 0
CELL_PARAMETERS
    3.5383398940    0.0000000000    0.0000000000
    0.0000000000    3.5383398940    0.0000000000
    0.0000000000    0.0000000000    3.5383398940

-------------- next part --------------
&CONTROL
	title = 'Bulk-Nickel',
	calculation = 'vc-relax',
 	restart_mode = 'from_scratch',
   	wf_collect = .true.,
	outdir = './temp',
	wfcdir = './wftemp',
	pseudo_dir = '/home/mmc14/pseudo',
       	prefix = 'Ni-bulk-pbe',
      	tstress = .true.,
      	tprnfor = .true.,
/
&SYSTEM
     	ibrav        = 0,
     	celldm(1)    = 1.889725989,
     	nat          = 1,
     	ntyp         = 1,
     	nbnd         = 30,
     	ecutwfc      = 40.0
     	ecutrho      = 320.0,
	occupations  ='smearing',
       	smearing     ='mp',
       	degauss      =0.005D0,
	nspin	     = 2,
       	starting_magnetization(1)=0.5,
/
&ELECTRONS
 	electron_maxstep = 100,
        conv_thr = 1.0D-8,
      	mixing_beta = 0.2
/
&IONS
     ion_dynamics = 'bfgs' ,
/
&CELL
               cell_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
	Ni1 58.6934   Ni.pbe-nd-rrkjus.UPF
ATOMIC_POSITIONS {alat}
Ni1      0.000000000   0.000000000   0.000000000
K_POINTS automatic
7 7 7   0 0 0
CELL_PARAMETERS
  18.516680427   0.000000000    0.000000000
   0.000000000  18.516680427    0.000000000
   0.000000000   0.000000000   18.516680427