The total energy is not variational with respect to the number of k-points, i.e. a lower total energy does not mean a better calculation when you compare 2 k-meshes. Clearly the 1000k calculation should be better.

PS: The size of the basis set is variational: a larger RKmax has to give you a lower energy.

PPS: As mentioned before, the GAP without spin-orbit is a meaningless number and you should NEVER say that the calculation which gives for the wrong reason the experimental gap is the "better" calculation.

Am 23.11.2016 um 13:15 schrieb Dr. K. C. Bhamu:
Dear Prof Peter,

Please comment of my query when you get time:This is in the queue on my
previous query regarding CH3NH3PbI3:


    I used two strategy and got different results:


    The experimental band gap is 1.67 eV for orthorhombic lead halide
    perovskite.

    I ran two cases (with PBE);
    1. with 1000 k, div: ( 11  7 11) and "min -j 'run_lapw -p -I -NI -i
    120 *-ec *0.00001 *-ec * 0.0001 -fc 1
    2. with 400 k, div: (  8  5  8)   and   min -j 'run_lapw -p -I -NI
    -i 120 *-ec * 0.0001 *-ec * 0.0005 -fc 2'

-ec switch is used twice instead of ec and cc (it is by mistake)
In case 2 with less k-points and normal scf criteria (-ec 0.0001 -ec
0.0005 -fc 2), I got minimized ENE than case 1. But the band gap is good
from case 1.


Results:

1. GAP 1.687 eV,    FER: 0.1030934295, ENE: -339059.11079128
2. GAP  1.777 eV,   FER: 0.1004906191, ENE: -339059.12432403

You see that band gap is in the error of /+- 0.01eV.

*[* next i tried with

1. with 1000 k, div: ( 11  7 11) and "min -j 'run_lapw -p -I -NI -i 120
-ec 0.00001 _-cc_ 0.0001 -fc 1   >> second -ec is replaced by -cc
2. with 400 k, div: (  8  5  8)   and   min -j 'run_lapw -p -I -NI -i
120 -ec 0.0001 _-cc _ 0.0005 -fc 2'      ***>> second -ec is replaced by
-cc*
*
*and nothing happened scf immediately got exit and the structure was
already optimized]*



    I did nothing special, just reduced rmt (5% and further rmt of "I"
    was reduced by 0.02).
    /_Please correct me what is wrong here. Because usually PBE always
    underestimates the experimental band gap._/

    Kind regards
    Bhamu




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Peter Blaha
Inst.Materials Chemistry
TU Vienna
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