occopt and nband Si.  [SOLVED]

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Gustavo Moneqz
Posts: 4
Joined: Tue Apr 02, 2019 3:46 am

occopt and nband Si.

Post by Gustavo Moneqz » Sun Apr 07, 2019 6:42 am

Hello everyone, I'm doing the ecut convergence study needed in the third tutorial, I'm trying to simulate an isolated molecule of Si, as done in tutorial I and II with the H.
When I run the program there are no results in the output file, and in the err file this message appears:

Initialization of occ, with occopt= 1
There are not enough bands to get charge balance right
Action: modify input file ...
(check the pseudopotential charges, the variable charge,
and the declared number of bands, nband)
...

I'm using occopt = 1 because I know is the value used for semiconductors, my question is:

How can I know the number of bands needed for a given element? In this case im using Si, but if I were using Co, Fe, or Cu how could I know?
here is the code I am doing:

Code: Select all

#I want an ecut convergence study
#Im simulating an isolated Si molecule, as done in I and II but with parameters for Si.

#Doing a double loop, with 10 data sets, one for the molecule and the other one for the isolated atom, im trying to reach ecut = 12, from ecut = 2 with steps with ecut =1.
 ndtset 10  udtset 5 2

#Here i define the ecut and acell, later i will optimize acell.
 acell 10 10 10
 ecut:? 2    ecut+? 1

#First data set, Find the best bond lenght for a Si molecule, and its asociated total energy.
   natom?1 2             # There are two atoms
  ionmov?1 2             # Use the modified Broyden algorithm
   ntime?1 10            # Maximum number of Broyden "timesteps"
  tolmxf?1 5.0d-5        # Stopping criterion for the geometry optimization : when
                         # the residual forces are less than tolmxf, the Broyden
                         # algorithm can stop
   xcart?1 -0.5  0.0 0.0 # The starting values of the
            0.5  0.0 0.0 # atomic coordinates
  toldff?1 5.0d-6        # Will stop the SCF cycle when, twice in a row,
                         # the difference between two consecutive evaluations of
                         # forces differ by less than toldff (in Hartree/Bohr)
   nband?8  8           # Just one band

#Second data set: To obtain the isolated atom total energy.
   natom?2 1             # There is one atom
   nsppol?2 2             # Spin-polarized calculation
   occopt?1 1             
   nband?2 1 1           # Number of bands for spin up and spin down
  toldfe?2 1.0d-6        # Will stop the SCF cycles when, twice in a row,
                         # the difference between two consecutive evaluations
                         # of total energy differ by less than toldfe (in Hartree)
                         # This value is way too large for most realistic studies of materials
  xcart?2 0.0 0.0 0.0   # The atom is located at the origin
  spinat?2 0.0 0.0 1.0   # Initialisation of spin

  rprim  0.0  0.5  0.5
           0.5  0.0  0.5
           0.5  0.5  0.0

#Types of atoms definition:
 ntypat 1
 znucl 14

#Atoms definition:
 typat 1 1

# K Points Grid Definition.
 kptopt 0 #Meter manualmente los puntos.
 nkpt 1  #Sólo un punto k es necesario para un sistema aislado

#SCF procedure definition:
 nstep 10
 # El toldfe se definió arriba.
 diemac 12.0




Thank you very much

ebousquet
Posts: 469
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: occopt and nband Si.  [SOLVED]

Post by ebousquet » Mon Apr 08, 2019 4:45 pm

Dear Gustavo,
You can let the code initializes nband automatically.
Otherwise, you need to know how much valence electrons you have in your pseudopotential and multiply it by the number of atoms of your cell.
Best wishes,
Eric

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