Hybrid functional calculation results show large difference with VASP

[Xiaoming Wang]

Hello,

I conducted PBE0 and HSE calculations on a cube of ~10*10*10 (perovskite). For comparison, I also did the calculations using VASP (gamma only). However, to my surprise, the band gap obtained by cp2k is about 0.5 eV (HSE)  and 0.8 eV(PBE0) smaller than by vasp. The vasp results agree well with literature. For the cp2k calculations, I have checked the convergence of the cutoffs and auxiliary basis sets. Since for my structure, the only available basis sets is DZVP within BASIS_MOLOPT, thus I could not find a way to increase the primary basis size. But I checked the PBE results with DZVP compared with those of VASP. The difference of the band gap is very small, say only 0.02 eV. So I think the DZVP basis set is OK for my system. The inputs of my calculations are as follows. Could anyone give me some suggestions?

HSE input:

--------------------------------------------------------------------

&GLOBAL

 PROJECT_NAME CsInAgCl

 RUN_TYPE ENERGY

 PRINT_LEVEL LOW

&END GLOBAL

&FORCE_EVAL

 METHOD QS

  &DFT

    BASIS_SET_FILE_NAME BASIS_MOLOPT

    BASIS_SET_FILE_NAME BASIS_ADMM

    BASIS_SET_FILE_NAME BASIS_ADMM_MOLOPT

    POTENTIAL_FILE_NAME GTH_POTENTIALS

    WFN_RESTART_FILE_NAME -PBE.wfn

    &QS

     EPS_PGF_ORB 1.0e-6

    &END

    &MGRID

      CUTOFF 250

      REL_CUTOFF 60

    &END MGRID

    &XC

      &XC_FUNCTIONAL

       &PBE

        SCALE_X 0.0

        SCALE_C 1.0

       &END PBE

       &XWPBE

        SCALE_X -0.25

        SCALE_X0 1.0

        OMEGA 0.11

       &END XWPBE

      &END XC_FUNCTIONAL

      &HF

       FRACTION 0.25

       &SCREENING

        EPS_SCHWARZ 1.0e-6

       &END SCREENING

       &INTERACTION_POTENTIAL

        POTENTIAL_TYPE SHORTRANGE

        OMEGA 0.11

       &END INTERACTION_POTENTIAL

       &MEMORY

        MAX_MEMORY 2400

        EPS_STORAGE_SCALING 0.1

       &END MEMORY

      &END HF

    &END XC

    &SCF

     #ADDED_MOS 2

      MAX_SCF 100

      EPS_SCF 1.0e-6

      CHOLESKY INVERSE

      SCF_GUESS RESTART

      &OT

       PRECONDITIONER FULL_ALL

       ENERGY_GAP 0.01

      &END OT

    &END SCF

    &AUXILIARY_DENSITY_MATRIX_METHOD

     METHOD BASIS_PROJECTION

     ADMM_PURIFICATION_METHOD MO_DIAG

    &END AUXILIARY_DENSITY_MATRIX_METHOD

    &PRINT

     &MO_CUBES

      WRITE_CUBE F

      NHOMO 1

      NLUMO 1

     &END MO_CUBES

    &END PRINT

  &END DFT

  &SUBSYS

    &CELL

      ABC [angstrom] 10.5345 10.5345 10.5345

      ALPHA_BETA_GAMMA [deg] 90 90 90

      PERIODIC XYZ

      SYMMETRY CUBIC

    &END CELL

    &COORD

     ....[I omitted the coors here ]

      SCALED T

    &END COORD

    &KIND Cs

      ELEMENT Cs

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT11

      POTENTIAL GTH-PBE-q9

    &END KIND

    &KIND In

      ELEMENT In

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT11

      POTENTIAL GTH-PBE-q13

    &END KIND

    &KIND Ag

      ELEMENT Ag

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT11

      POTENTIAL GTH-PBE-q11

    &END KIND

    &KIND Cl

      ELEMENT Cl

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT3

      POTENTIAL GTH-PBE-q7

    &END KIND

  &END SUBSYS

&END FORCE_EVAL

-----------------------------------------------------------------------------------------------

PBE0 input

--------------------------------------------------------

&GLOBAL

 PROJECT_NAME CsInAgCl

 RUN_TYPE ENERGY

 PRINT_LEVEL LOW

&END GLOBAL

&FORCE_EVAL

 METHOD QS

  &DFT

    BASIS_SET_FILE_NAME BASIS_MOLOPT

    BASIS_SET_FILE_NAME BASIS_ADMM

    BASIS_SET_FILE_NAME BASIS_ADMM_MOLOPT

    POTENTIAL_FILE_NAME GTH_POTENTIALS

    WFN_RESTART_FILE_NAMEPBE.wfn

    &QS

     EPS_PGF_ORB 1.0e-6

    &END

    &MGRID

      CUTOFF 250

      REL_CUTOFF 60

    &END MGRID

    &XC

      &XC_FUNCTIONAL

       &PBE

        SCALE_X 0.75

        SCALE_C 1.0

       &END PBE

       &PBE_HOLE_T_C_LR

        CUTOFF_RADIUS 5.25

        SCALE_X 0.25

       &END PBE_HOLE_T_C_LR

      &END XC_FUNCTIONAL

      &HF

       FRACTION 0.25

       &SCREENING

        EPS_SCHWARZ 1.0e-6

       &END SCREENING

       &INTERACTION_POTENTIAL

        POTENTIAL_TYPE TRUNCATED

        CUTOFF_RADIUS 5.25

        T_C_G_DATA ./t_c_g.dat

       &END INTERACTION_POTENTIAL

       &MEMORY

        MAX_MEMORY 2400

        EPS_STORAGE_SCALING 0.1

       &END MEMORY

      &END HF

    &END XC

    &SCF

      MAX_SCF 100

      EPS_SCF 1.0e-6

      CHOLESKY INVERSE

      SCF_GUESS RESTART

      &OT

       PRECONDITIONER FULL_ALL

       ENERGY_GAP 0.01

      &END OT

    &END SCF

    &AUXILIARY_DENSITY_MATRIX_METHOD

     METHOD BASIS_PROJECTION

     ADMM_PURIFICATION_METHOD MO_DIAG

    &END AUXILIARY_DENSITY_MATRIX_METHOD

    &PRINT

     &MO_CUBES

      WRITE_CUBE F

      NHOMO 1

      NLUMO 1

     &END MO_CUBES

    &END PRINT

  &END DFT

  &SUBSYS

    &CELL

      ABC [angstrom] 10.5345 10.5345 10.5345

      ALPHA_BETA_GAMMA [deg] 90 90 90

      PERIODIC XYZ

      SYMMETRY CUBIC

    &END CELL

    &COORD

       .......

      SCALED T

    &END COORD

    &KIND Cs

      ELEMENT Cs

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT11

      POTENTIAL GTH-PBE-q9

    &END KIND

    &KIND In

      ELEMENT In

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT11

      POTENTIAL GTH-PBE-q13

    &END KIND

    &KIND Ag

      ELEMENT Ag

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT11

      POTENTIAL GTH-PBE-q11

    &END KIND

    &KIND Cl

      ELEMENT Cl

      BASIS_SET DZVP-MOLOPT-SR-GTH

      AUX_FIT_BASIS_SET FIT3

      POTENTIAL GTH-PBE-q7

    &END KIND

  &END SUBSYS

&END FORCE_EVAL

--------------------------------------

I have attached my benchmark tests.

Best,

Xiaoming Wang

  

[Marcella Iannuzzi]

Hi, 

Your eps_schwarz at 1.0e-6 is far too large.

The default is 1.0e-10. 

Regards

Marcella

Best,

Xiaoming Wang

  

[Xiaoming Wang]

Hi Marcella,

Thanks for your reply. I have checked that parameter. Actually, eps_schwarz of 1.0e-10 give quite a small improvement of the band gap, ~0.01 eV. Any other suggestions?

Best,

Xiaoming 

[Nico Holmberg]

Hi,

You should try switching off ADMM purification i.e. setting ADMM_PURIFICATION_METHOD NONE. According to the implementation paper, this is the correct way to obtain MO energies. A direct quote from the implementation paper: "In order to use the eigenvalues of the ADMM Kohn-Sham matrix directly as orbital energies, e.g., to calculate the band gaps of a system, an ADMM scheme without purification needs to be employed."

You can find TZVP-MOLOPT quality basis sets for Ag, Cs, and In in the BASIS_MOLOPT_UCL file distributed with the trunk version of cp2k if you want to test the effect of using larger primary basis sets.


BR,

Nico

[Xiaoming Wang]

Hi, Nico,

Thanks for your reply. 

I did tried the case without ADMM_PURIFICATION, but the band gap is only 0.01 eV smaller. As for the basis set, I don't know whether it would affect the HFX electronic structure or not. But for GW calculations, the completeness of the basis set plays an important role. I will try the TZVP basis to see what happens.

Best,

Xiaoming

[Xiaoming Wang]

Hi,

I checked the convergence of the primary basis size. To be specific, I compared the DZVP and TZVP basis sets. The difference of the PBE band gap is within 0.01 eV.  The PBE0 band gap without coulomb trunction also shows small difference, say ~0.01 eV. The band gap variation by coulomb truncation as in PBE0-TC-LRC scheme is larger, say 0.05 eV, but still not too much.  

Any other advice?

Best,

Xiaoming

[Marcella Iannuzzi]

Hi, 

Can you test your system without ADMM? (maybe a smaller version of it)

You should compare the electronic properties obtained with and without ADMM to verify whether the problems is there or somewhere else.

Regards

Marcella

[Xiaoming Wang]

Hi Marcella,

What do you mean by the 'smaller version'? If you are meaning a smaller basis set for ABS, I did the test. To my surprise, the results don't change much when I go to the smallest ABS, say cFIT3 for Cl, cFIT9 for Ag and In, cFIT7 for Cs. Is this behavior reasonable? 

Without ADMM, it seems that the computation would take extremely long time with the same cpu cores. With ADMM, I can finish the calculation within couple of minutes. However, without ADMM, it has taken me almost one hour and the first OT step hasn't even appear in the output. Does this sounds reasonable as well?

Best,

Xiaoming 

[hut...@chem.uzh.ch]

Hi

I would first try a larger ADMM basis, e.g. pFIT3.

The increase in CPU time for a full exchange calculation with
MOLOPT basis sets can be 100x - 1000x.

regards

Juerg
--------------------------------------------------------------
Juerg Hutter Phone : ++41 44 635 4491
Institut für Chemie C FAX : ++41 44 635 6838
Universität Zürich E-mail: hut...@chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp...@googlegroups.com wrote: -----To: cp2k <cp...@googlegroups.com>
From: Xiaoming Wang
Sent by: cp...@googlegroups.com
Date: 09/19/2017 04:46PM
Subject: [CP2K:9441] Re: Hybrid functional calculation results show large difference with VASP

Hi Marcella,
What do you mean by the 'smaller version'? If you are meaning a smaller basis set for ABS, I did the test. To my surprise, the results don't change much when I go to the smallest ABS, say cFIT3 for Cl, cFIT9 for Ag and In, cFIT7 for Cs. Is this behavior reasonable?
Without ADMM, it seems that the computation would take extremely long time with the same cpu cores. With ADMM, I can finish the calculation within couple of minutes. However, without ADMM, it has taken me almost one hour and the first OT step hasn't even appear in the output. Does this sounds reasonable as well?
Best,Xiaoming

On Tuesday, September 19, 2017 at 4:58:43 AM UTC-4, Marcella Iannuzzi wrote:Hi,

Can you test your system without ADMM? (maybe a smaller version of it)You should compare the electronic properties obtained with and without ADMM to verify whether the problems is there or somewhere else.RegardsMarcella

On Tuesday, September 19, 2017 at 8:23:59 AM UTC+2, Xiaoming Wang wrote:Hi,
I checked the convergence of the primary basis size. To be specific, I compared the DZVP and TZVP basis sets. The difference of the PBE band gap is within 0.01 eV. The PBE0 band gap without coulomb trunction also shows small difference, say ~0.01 eV. The band gap variation by coulomb truncation as in PBE0-TC-LRC scheme is larger, say 0.05 eV, but still not too much.
Any other advice?
Best,Xiaoming

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[Xiaoming Wang]

Hi,

Thanks for pointing out the time estimate for me. The largest ADMM basis I can afford is FIT11 for Cs, Ag, In and pFIT3 for Cl. Also with these larger basis, the band gap change is quite small, say 0.015 eV. With larger ADMM basis, the band gap tends to be slightly smaller, contrary to the case of Si. Is the behavior of nonsensitive dependence on the ADMM basis related to the high ionicity of the present structure?

Best,

Xiaoming

[Xiaoming Wang]

Hi,

I have done more comparisons of the band gap obtained by CP2K and VASP. I tested Si and NaCl, both with the basis set from BASIS_MOLOPT, BASIS_ADMM and GTH-PBE potentials. In these cases, the band gap agrees well, only ~0.1 eV difference. Does this mean that the large discrepancy of my previous case is due to basis set of Cs, Ag and In?

Best,

Xiaoming   

[hut...@chem.uzh.ch]

Hi

If the problem is the orbital basis of this elements, you would see
a difference also for the PBE gap. If the PBE gap is ok, but the
PBE0/HSE gap is wrong, it is most likely the ADMM basis of these
elements.

regards

Juerg
--------------------------------------------------------------
Juerg Hutter Phone : ++41 44 635 4491
Institut für Chemie C FAX : ++41 44 635 6838
Universität Zürich E-mail: hut...@chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp...@googlegroups.com wrote: -----To: cp2k <cp...@googlegroups.com>
From: Xiaoming Wang
Sent by: cp...@googlegroups.com

Date: 09/19/2017 11:55PM
Subject: [CP2K:9447] Re: Hybrid functional calculation results show large difference with VASP

Hi,
I have done more comparisons of the band gap obtained by CP2K and VASP. I tested Si and NaCl, both with the basis set from BASIS_MOLOPT, BASIS_ADMM and GTH-PBE potentials. In these cases, the band gap agrees well, only ~0.1 eV difference. Does this mean that the large discrepancy of my previous case is due to basis set of Cs, Ag and In?

[Xiaoming Wang]

Hi,

I agree with you that the problem is most likely due to the ADMM basis, and more tests shows that it is the ADMM basis of In and Ag causing the large discrepancy. Maybe the problem of d orbitals?  I tested PBE0 calculations of NaCl, CsCl, AgCl, and InCl3 by CP2K and VASP. The band gap of both NaCl and CsCl show quite small difference between the two codes, say ~0.01-0.02 eV. However, AgCl and InCl3 exhibit relative larger discrepancy, with AgCl 0.16 eV discrepancy and InCl3 0.18 eV, CP2K results of both are smaller than VASP.  For my system, I have both Ag and In, so I think the errors added up.  Any advice on how to improve the ADMM basis set?

Best,

Xiaoming

[S Ling]

Hi

I am not sure whether you are using the same ADMM basis sets (see your initial input) for these new test calculations. One thing which I can see is that you are not using the largest available ADMM basis sets for some of the elements, e.g. the largest available ADMM basis sets for Cl, Ag and In are pFIT3, FIT12 and FIT13, respectively. Taking In as an example, the FIT13 ADMM basis set of In contains more p and d functions than FIT11, which may be important for your system. 

You mentioned a few different functionals, including PBE, PBE0 and HSE06, and you have run quite a lot of benchmark tests. It would help if you can tabulate all the numbers you have got (including the reference), so we can understand your problem better.

In addition, I can see you're using a CUTOFF of 250 Ry. Please also check whether your calculation is converged with respect to this parameter.

Please also keep in mind that CP2K and VASP use different pseudopotentials and basis sets. I wouldn't expect the two codes to give the same numbers for your target properties. If you look into literatures, you will also find people reporting different numbers for the same property using the same method and code.

SL

 

[Xiaoming Wang]

Hi Ling,

Thanks for your comments. I have attached my benchmark results here.  Based on my tests, it seems that the ADMM basis set size is not so important for ionic crystals. One can get reasonable results even with smallest basis sets. Btw, the cutoff and rel_cutoff used are well converged values for my target property. So I think there is still room to improve the ADMM basis for Ag and In (with semicore d states in the valence). To check whether it is the problem of Ag and In ADMM basis, the simplest way is to do the PBE0 calculations without ADMM. But the calculation takes me too long time, as also pointed out by Juerg. I suspect if it is possible to do HFX without ADMM using MOLOPT basis sets.

Best,

Xiaoming

[Matt W]

That ADMM basis is already pretty large, so whilst it might be the problem, first I'd check the cell size.

Can you build a cell about 15 x 15 x 15 A or larger to allow you to extend the range of the hybrid out to 6 or 7 A?

You are truncating at about 5.25 A, which might not be enough to be fully converged (note VASP won't be doing this as it works in K space). 

Matt 

[Xiaoming Wang]

Hi Matt,

Actually I also did the calculation for a supercell of 21*21*21 with 320 atoms. PBE0 without TC are also tested, please see my benchmark tests in previous post (attachment in reply to Ling).

Best,

Xiaoming

[Matt W]

Hi,

I only see the check for InCl3, not the main system?

Matt

[Xiaoming Wang]

Hi, Can you see it this time?

[S Ling]

Hi

Can you confirm the chemical formula of your CsInAgCl system? I looked through the ICSD database, and the only related compound which I can find is CsAgInF6, in which Ag is in an uncommon +2 oxidation state (in your benchmark test, you looked at AgCl, in which Ag is in the common +1 oxidation state). If this is the case for CsInAgCl6, there is a possibility that your CP2K/PBE0 and VASP/PBE0 calculations may have converged to slightly different SCF solutions. You can check this by comparing the orbital occupation numbers from your VASP/PROCAR and from the CP2K/PDOS analysis. Another possibility is that the ADMM basis sets are indeed not good enough to describe Ag2+ (I have only considered Ag+ when I was fitting the ADMM basis sets of Ag).

SL

 

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[Xiaoming Wang]

Hi,

I am sorry for the confusing formula. It is actually Cs2InAgCl6, in which Ag is +1. When you are fitting the ADMM basis sets, what's the reference system for Ag?  Is it in solid environment? Is it possible for me to fit the ADMM basis myself based on my vasp calculations? Well, maybe it is too difficult for me, since I am new to cp2k. Btw, do the ADMM basis sets depend on the oxidation states of the elements involved? If that's the case, there would be problems dealing with different systems with the same basis sets. Moreover, the oxidation state is an arbitrary quantity depending on the charge partition scheme. The oxidation state may be slight different even for the systems which are assumed to be +1 for a particular element, for example.

Best,

Xiaoming  

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[Xiaoming Wang]

I'd like to add that my PBE0 calculation without ADMM basis sets has been done. I tested 10*10*10 Cs2InAgCl6, which is the system of my original post. The band gap is 2.52 and 2.50 eV for with and without ADMM. So it seems not the ADMM basis problem?  

I have another question that without ADMM basis sets I have SCF convergence issue if I don't use the Coulomb truncation method, both for OT and diagonalization, the SCF didn't tend to converge. Why is that? (The calculation is fine with TC.)

Best,

[S Ling]

Hi

I am not sure how you ran the PBE0 calculation without ADMM using the MOLOPT basis sets, which were not designed for hybrid DFT calculations. Hybrid DFT calculations without ADMM for your Cs2InAgCl6 system will use a lot of memory, and as Prof Hutter suggested earlier, it will also be 100~1000 times slower.

"without ADMM basis sets I have SCF convergence issue if I don't use the Coulomb truncation method, both for OT and diagonalization, the SCF didn't tend to converge. Why is that?"

Please have a look at the two papers below, which answer your question:

http://pubs.acs.org/doi/abs/10.1021/ct900494g

http://aip.scitation.org/doi/10.1063/1.2931945

For the PBE0 band gaps calculated using different codes, I can see for binary systems, the differences are at the order of 0.2 eV or smaller, which I think is not something totally unexpected, because of the different HFX implementation strategies, different basis sets and different pseudopotentials used by the two codes. If you try a third code based on atomic orbital basis sets, you may also get different answers. In addition, similar results at PBE level doesn't necessarily mean the numbers at PBE0 level will or should be similar as well. From computational point of view, compounds involving d block elements are usually more difficult to deal with than compounds involving only s and p block elements. As you mentioned earlier, it could simply be the case that the differences in binary systems added up in your quaternary system. It may be useful to check what numbers the two codes will give for the ternary system, before we look at the more complicated quaternary system. The VASP/PROCAR and CP2K/PDOS analysis will tell us what are the nature of the states at the top of the valence band and at the bottom of the conduction band, which will help us to understand the difference between the two codes.

SL

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[Vladimir Rybkin]

Dear Xiaoming Wang,

that's why the truncation operator for the exchange integrals is introduced. Please, have a look at reference:
http://pubs.acs.org/doi/abs/10.1021/ct900494g

Yours,

Vladimir

четверг, 21 сентября 2017 г., 15:57:45 UTC+2 пользователь Xiaoming Wang написал:

[Xiaoming Wang]

Hi Ling,

Here is my input for PBE0 calculation without ADMM.

-------------------------------------------------------------------------------

&GLOBAL

 PROJECT_NAME Cs2InAgCl6

 RUN_TYPE ENERGY

 PRINT_LEVEL LOW

&END GLOBAL

&FORCE_EVAL

 METHOD QS

  &DFT

    BASIS_SET_FILE_NAME BASIS_MOLOPT

    POTENTIAL_FILE_NAME GTH_POTENTIALS

    WFN_RESTART_FILE_NAME pbe.wfn

    &QS

     EPS_DEFAULT 1.0e-10

     EPS_PGF_ORB 1.0e-6

    &END

    &MGRID

      CUTOFF 250

      REL_CUTOFF 50

    &END MGRID

    &XC

      &XC_FUNCTIONAL

       &PBE

        SCALE_X 0.75

        SCALE_C 1.0

       &END PBE

       &PBE_HOLE_T_C_LR

        CUTOFF_RADIUS 5

        SCALE_X 0.25

       &END PBE_HOLE_T_C_LR

      &END XC_FUNCTIONAL

      &HF

       FRACTION 0.25

       &SCREENING

        EPS_SCHWARZ 1.0e-6

       &END SCREENING

       &INTERACTION_POTENTIAL

        POTENTIAL_TYPE TRUNCATED

        CUTOFF_RADIUS 5

        T_C_G_DATA ./t_c_g.dat

       &END INTERACTION_POTENTIAL

       &MEMORY

        MAX_MEMORY 3200

        EPS_STORAGE_SCALING 0.1

       &END MEMORY

      &END HF

    &END XC

    &SCF

      MAX_SCF 100

      EPS_SCF 1.0e-6

      CHOLESKY INVERSE

      SCF_GUESS RESTART

      &DIAGONALIZATION

       ALGORITHM STANDARD

      &END DIAGONALIZATION

      &MIXING

       METHOD PULAY_MIXING

    &END SCF

    &PRINT

     &MO_CUBES

      WRITE_CUBE F

      NHOMO 1

      NLUMO 1

     &END MO_CUBES

    &END PRINT

  &END DFT

  &SUBSYS

    &CELL

      ABC [angstrom] 10.5345 10.5345 10.5345

      ALPHA_BETA_GAMMA [deg] 90 90 90

      PERIODIC XYZ

      SYMMETRY CUBIC

    &END CELL

    &COORD

       ............

      SCALED T

    &END COORD

    &KIND Cs

      ELEMENT Cs

      BASIS_SET DZVP-MOLOPT-SR-GTH

      POTENTIAL GTH-PBE-q9

    &END KIND

    &KIND In

      ELEMENT In

      BASIS_SET DZVP-MOLOPT-SR-GTH

      POTENTIAL GTH-PBE-q13

    &END KIND

    &KIND Ag

      ELEMENT Ag

      BASIS_SET DZVP-MOLOPT-SR-GTH

      POTENTIAL GTH-PBE-q11

    &END KIND

    &KIND Cl

      ELEMENT Cl

      BASIS_SET DZVP-MOLOPT-SR-GTH

      POTENTIAL GTH-PBE-q7

    &END KIND

  &END SUBSYS

&END FORCE_EVAL

I have the PROCAR file from VASP calculations. I need to find a way to get the PDOS from cp2k. I will post the results later.

Best,

Xiaoming

[Xiaoming Wang]

Hi Vladimir,

Thanks for the reference.

Best,

[Xiaoming Wang]

Hi,

Here is PBE0 PDOS of HOMO and LUMO of Cs2InAgCl6.

		CP2K			VASP
		s	p	d	s	p	d
HOMO	Cs	0.000	0.000	0.000	0.000	0.000	0.000
	In	0.000	0.000	0.050	0.000	0.000	0.030
	Ag	0.000	0.000	0.454	0.000	0.000	0.368
	Cl	0.003	0.488	0.004	0.000	0.456	0.000
LUMO	Cs	0.085	0.000	0.000	0.000	0.000	0.000
	In	0.300	0.000	0.000	0.332	0.000	0.000
	Ag	0.241	0.000	0.000	0.212	0.000	0.000
	Cl	0.194	0.074	0.107	0.096	0.048	0.024

I will also try to do a ternary system like CsPbBr3.

I have another question for Cs2InAgCl6. You are saying that Ag is optimized for +1. What I am going to study is the hole state of Cs2InAgCl6, so one electron will be removed from the system. In that case, Ag will tend to be in 2+ state. Can you comment on the reliability of the PBE0 calculation if I focus on the structure instead of  the band gap? 

Best,

[S Ling]

Hi

Looks like you may changed your input from the initial one slightly: the PDOS analysis shows you are running spin polarised calculations (at least for CP2K, as the sum equals to 1; you didn't include UKS or LSD in your initial input). For the analysis on VASP calculation, are these numbers correspond to all the atoms in the cell or just part of it? The sum of the numbers doesn't equal to 1 or 2, so we cannot see what are the real differences.

"I will also try to do a ternary system like CsPbBr3."

From your benchmark data, I would be more worried about In and Ag. I cannot find any ternary halide involving Ag and In, but you can find AgInS2 from ICSD database. I think this may be a better system to test. You may also try CsAgX and CsInX.

"I have another question for Cs2InAgCl6. You are saying that Ag is optimized for +1. What I am going to study is the hole state of Cs2InAgCl6, so one electron will be removed from the system. In that case, Ag will tend to be in 2+ state. Can you comment on the reliability of the PBE0 calculation if I focus on the structure instead of  the band gap?"

I think the uncontracted ADMM basis sets (FIT??, not cFIT??) should be flexible enough to describe Ag2+. From your CP2K/PDOS analysis, it looks like there may be a competition in terms of hole localisation, as the HOMO features mixed Ag+ and Cl- states. I am not sure how the smaller band gap in CP2K (compared with your reference) will affect hole localisation in Cs2InAgCl6. Again, I would start from a simpler binary system as a testbed, e.g. AgCl, which I am sure has been studied before, I would use the same PBE0-TC functional, and I would then compare the hole localisation properties (e.g. self-trapping energy, etc) of AgCl with previous literatures. Once I am happy with the results on binary system, I would then feel more comfortable to move to the more complicated ternary and quaternary systems.

An additional test you can try is to relax the cell paramters and atomic positions of Cs2InAgCl6 in CP2K at PBE0-TC level, and see if that improves the agreement with the experimental value on band gap. I was looking at a JPCL paper (DOI: 10.1021/acs.jpclett.6b02682) on Cs2InAgCl6, and it looks like the authors reported a range (2.9~3.3 eV) of band gap values at PBE0 level for Cs2InAgCl6 with different geometry relaxations. This actually shows the band gap is quite sensitive to small differences in geometries.

It looks like this discussion has become quite technical now. I am happy to continue the discussion offline if you are interested.

SL

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