[CP2K-user] [CP2K:17073] Re: Density of states with k-points in CP2K

[Nicholas Winner]

It is a static calculation, so iteration = 0. I redid the calculation with 
cell optimization. Didn't seem much of change. Here at the plots using the 
occupation first and the density second. I set fermi level to be 0, and it 
doesn't put it anywhere near the VBM like we expect. In the second case it 
looks like there is a gap, but its too big. 

Any knowledge maybe about the definition of fermi level? Maybe that's where 
I'm tripping up.
[image: Screen Shot 2022-06-02 at 1.00.02 PM.png]
Do you know anything about the fermi level definition?
[image: Screen Shot 2022-06-02 at 12.59.51 PM.png]
On Thursday, June 2, 2022 at 9:04:42 AM UTC-7 wave... at gmail.com wrote:

> Hi
>
> It's not clear to me why you are looking at the first step. Did it 
> converge in just one step?
>
> At any rate, you'll notice a difference between &DOS and &PDOS. PDOS 
> returns values per orbital (s, p, d, f). If I understand it correctly, the 
> density is the DOS as a solid state physicist would understand it, and 
> occupation gives you a fractional filling at that energy. Not quite the 
> same thing.
>
> Regards
> Sam
>
> On Wednesday, June 1, 2022 at 7:39:20 PM UTC+2 nwi... at berkeley.edu wrote:
>
>> Hi everyone, 
>>
>> I know that DOS and points aren't what people first think of when using 
>> cp2k, but the functionality does seem to be there in some limited way... 
>>
>> Anyway, I'm wondering how to properly use it, because my test case 
>> doesn't look right. I'm running a point calculation on GaAs with a 16x16x16 
>> Monkhorst-Pack pack grid and then printing the total DOS. I then take the 
>> columns from the DOS file (head attached) and plot energy (column 1) 
>> against occupation (column 3) using the reported Fermi energy from the 
>> output file of ~0.14 Ha. This results in a DOS where the Fermi energy does 
>> not line up with the VBM. What's more, if I visually inspect this DOS, the 
>> band gap of GaAs is >1eV. While that is closer to the experimental value, 
>> the reported band gap using GGA PBE is closer to 0.3eV.  
>>
>> Questions:
>> (1) What is the distinction between columns 2 and 3 in the DOS file? They 
>> give similar, but not equivalent looking dos plots.
>> (2) Is the Fermi energy printed in the output file the same as the Fermi 
>> energy of the DOS, or is it defined different?
>>
>> I've attached my input file for reference. Thanks in advance.
>>
>>  # DOS at iteration step i = 0
>>
>>     Energy[a.u.]       Density     Occupation
>>
>>     -0.40682067         0.0009         0.0957
>>
>>     -0.40582067         0.0015         0.1543
>>
>>     -0.40482067         0.0000         0.0000
>>
>>     -0.40382067         0.0000         0.0000
>>
>>     -0.40282067         0.0034         0.3516
>>
>>     -0.40182067         0.0026         0.2656
>>
>>     -0.40082067         0.0038         0.3828
>>
>>     -0.39982067         0.0000         0.0000
>>
>> [image: Screen Shot 2022-06-01 at 10.32.10 AM.png]
>>
>

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