[QE-users] problems in graphene simulation
Christoph Wolf
wolf.christoph at qns.science
Fri Sep 27 13:10:29 CEST 2019
Getting the correct band gap from DFT is usually a coincidence due to the
approximations made in exchange and correlation potential.
You can try GW calculations on top of the DFT ground state, in QE you can
use YAMBO. In addition to the above you also have to consider if your
experimental value is a single particle excitation or a two particle
(electron hole excitation). In the latter case you might need to solve the
BSE.
Hth
Chris
On Fri, Sep 27, 2019, 7:01 PM <users-request at lists.quantum-espresso.org>
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> Today's Topics:
>
> 1. What Is Estimated SCF Accuracy (Ben Comer)
> 2. Re: What Is Estimated SCF Accuracy (Paolo Giannozzi)
> 3. Re: What Is Estimated SCF Accuracy (Ben Comer)
> 4. VC-relax in polar materials (Eric Glen Suter)
> 5. Convergence of Ecutwfc and Ecutrho for Doublet Occupation
> Scheme (Brendan Smith)
> 6. Re: What Is Estimated SCF Accuracy (Ben Comer)
> 7. Re: What Is Estimated SCF Accuracy (Paolo Giannozzi)
> 8. problems in graphene simulation (Haider Abbas)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 26 Sep 2019 14:51:42 +0000
> From: Ben Comer <bcomer3 at gatech.edu>
> To: "users at lists.quantum-espresso.org"
> <users at lists.quantum-espresso.org>
> Subject: [QE-users] What Is Estimated SCF Accuracy
> Message-ID: <7746af3e-46b8-bfcb-734c-66a97822c65f at gatech.edu>
> Content-Type: text/plain; charset="utf-8"
>
> Hello,
>
> I'm trying to understand what exactly estimated SCF accuracy is. Does
> anyone know where I can find a formal definition of what it is and how
> it is being calculated? The structure of the output file implies that it
> is related to the Harris-Foulkes and the total energy, but it is clearly
> not the trivial difference between these two quantities.
>
> Thanks in advance,
> Ben Comer
> Georgia Tech
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 26 Sep 2019 16:57:46 +0200
> From: Paolo Giannozzi <p.giannozzi at gmail.com>
> To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
> Subject: Re: [QE-users] What Is Estimated SCF Accuracy
> Message-ID:
> <CAPMgbCurAsE9CU_XF7h5jE38p=
> u1g8aMJTT51-_7SCyorG4kww at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> If I remember correctly: Eq.A6 of J.Phys.: Condens. Matter 21, 395502
> (2009)
>
> Paolo
>
> On Thu, Sep 26, 2019 at 4:52 PM Ben Comer <bcomer3 at gatech.edu> wrote:
>
> > Hello,
> >
> > I'm trying to understand what exactly estimated SCF accuracy is. Does
> > anyone know where I can find a formal definition of what it is and how
> > it is being calculated? The structure of the output file implies that it
> > is related to the Harris-Foulkes and the total energy, but it is clearly
> > not the trivial difference between these two quantities.
> >
> > Thanks in advance,
> > Ben Comer
> > Georgia Tech
> >
> > _______________________________________________
> > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso
> )
> > users mailing list users at lists.quantum-espresso.org
> > https://lists.quantum-espresso.org/mailman/listinfo/users
> >
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
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> ------------------------------
>
> Message: 3
> Date: Thu, 26 Sep 2019 15:22:44 +0000
> From: Ben Comer <bcomer3 at gatech.edu>
> To: "users at lists.quantum-espresso.org"
> <users at lists.quantum-espresso.org>
> Subject: Re: [QE-users] What Is Estimated SCF Accuracy
> Message-ID: <ef6ec918-7a31-bda6-54d2-fb77941b3986 at gatech.edu>
> Content-Type: text/plain; charset="utf-8"
>
> Thanks this answered my question, the responses are much appreciated!
>
> On 9/26/19 10:58 AM, Stefano de Gironcoli wrote:
> > In the simplest case it is the electrostatic self energy of the
> > difference between rho_in and rho_out and as such it is an estimate of
> > the energy error. in more complex cases (magnetic systems, lda+u, ...)
> > it is modified in the same spirit.
> >
> > stefano
> >
> > On 26/09/19 16:51, Ben Comer wrote:
> >> Hello,
> >>
> >> I'm trying to understand what exactly estimated SCF accuracy is. Does
> >> anyone know where I can find a formal definition of what it is and how
> >> it is being calculated? The structure of the output file implies that it
> >> is related to the Harris-Foulkes and the total energy, but it is clearly
> >> not the trivial difference between these two quantities.
> >>
> >> Thanks in advance,
> >> Ben Comer
> >> Georgia Tech
> >>
> >> _______________________________________________
> >> Quantum ESPRESSO is supported by MaX
> >> (www.max-centre.eu/quantum-espresso)
> >> users mailing list users at lists.quantum-espresso.org
> >> https://lists.quantum-espresso.org/mailman/listinfo/users
>
> ------------------------------
>
> Message: 4
> Date: Thu, 26 Sep 2019 16:02:08 +0000
> From: Eric Glen Suter <esuter at uga.edu>
> To: "users at lists.quantum-espresso.org"
> <users at lists.quantum-espresso.org>
> Subject: [QE-users] VC-relax in polar materials
> Message-ID:
> <
> SN4PR0201MB34227CBF8D88B6F581A9C4DBD3860 at SN4PR0201MB3422.namprd02.prod.outlook.com
> >
>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hello all,
>
> I'm attempting to apply DFT calculations to a ferroelectric phase of a
> material. Are there special considerations to pay attention to when doing
> structural calculations on system like this? For instance, do we expect
> that a standard vc-relax will find a ferroelectric state of the material?
>
> I've seen some discussion on the use of the Berry phase options to
> calculate the polarization of the material, but is that necessary to
> include in order to get a satisfactory structure?
>
> Thanks in advance for any insights you can offer.
>
> Best regards,
>
> Eric Suter
>
> ----------------------------
>
> PhD Candidate, Dept. of Physics and Astronomy
>
> Center for Simulational Physics
>
> University of Georgia
>
> ----------------------------
>
> email: esuter at uga.edu
>
> phone: 912-856-3071
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> ------------------------------
>
> Message: 5
> Date: Thu, 26 Sep 2019 13:33:34 -0400
> From: Brendan Smith <bsmith24 at buffalo.edu>
> To: users at lists.quantum-espresso.org
> Subject: [QE-users] Convergence of Ecutwfc and Ecutrho for Doublet
> Occupation Scheme
> Message-ID:
> <CAOnTLZTsqhvhNncFqxxHg0_YT=
> 6eVBza9vH4wJ8rg4uLjXYmig at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi QE Experts,
>
> I have a system whose ground state is a doublet ( 1 spin up electron, in
> this case ). I am using ultrasoft PPs. The system is a 3x3x3 super cell of
> diamond with a single NV center.
>
> My strategy for converging Ecutwfc and Ecutrho follows the prescription
> laid out by Stephano in previous exchanges on the forum. It involves two
> steps:
>
> 1) Using the default Ecutrho = 4*Ecutwfc, I converge the total force of my
> cell w.r.t Ecutwfc.
>
> 2) Then, using the converged value of Ecutho, I scale back Ecutwfc to see
> how low I can get it without coming out of my tolerance window, which is
> 1mRy in the total force computed using the converged parameters.
>
> When I make my unit cell charged (therefore a triplet ground state [2 spin
> up electrons] ) - I get a great convergence.
>
> However, when doing step1 using my charge neutral (doublet) ground state, I
> obtain the following for step 1 in the convergence procedure:
>
> 20.0000 0.238517
> 30.0000 0.273459
> 40.0000 0.272399
> 50.0000 0.270205
> 60.0000 0.269809
> 70.0000 0.269807
> 80.0000 0.274589
> 90.0000 0.274698
> 100.0000 0.270163
> 110.0000 0.270168
> 120.0000 0.270176
> 130.0000 0.270245
> 140.0000 0.274755
> 150.0000 0.270246
>
> The left column is Ecut (Ry), the right column is Total Force (Ry/Bohr).
> One can notice "spikes", for example, at Ecut = 140, and E cut = 80-90 Ry.
>
> Can such a thing happen for a particular difficult occupation scheme? I
> suspect that I am oscillating between two solutions, and that using Ecut 50
> (therefore Ecutrho = 200 Ry) works here. Then, using Ecutrho = 200, I can
> most likely get the Ecutwfc back to ~ 35 or so.
>
> Thank you for your time,
> Best,
> Brendan A. Smith
>
> 4th year graduate student studying computational chemistry at the State
> University of New York at Buffalo
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> ------------------------------
>
> Message: 6
> Date: Thu, 26 Sep 2019 19:43:57 +0000
> From: Ben Comer <bcomer3 at gatech.edu>
> To: "users at lists.quantum-espresso.org"
> <users at lists.quantum-espresso.org>
> Subject: Re: [QE-users] What Is Estimated SCF Accuracy
> Message-ID: <83376ab5-076f-7abe-ad6c-269d40a530d8 at gatech.edu>
> Content-Type: text/plain; charset="utf-8"
>
> Just a quick follow up, the text seems to imply that A7 is used rather
> than A6. do you know where this is defined in the source code?
>
> On 9/26/19 10:57 AM, Paolo Giannozzi wrote:
> If I remember correctly: Eq.A6 of J.Phys.: Condens. Matter 21, 395502
> (2009)
>
> Paolo
>
> On Thu, Sep 26, 2019 at 4:52 PM Ben Comer <bcomer3 at gatech.edu<mailto:
> bcomer3 at gatech.edu>> wrote:
> Hello,
>
> I'm trying to understand what exactly estimated SCF accuracy is. Does
> anyone know where I can find a formal definition of what it is and how
> it is being calculated? The structure of the output file implies that it
> is related to the Harris-Foulkes and the total energy, but it is clearly
> not the trivial difference between these two quantities.
>
> Thanks in advance,
> Ben Comer
> Georgia Tech
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso<
> http://www.max-centre.eu/quantum-espresso>)
> users mailing list users at lists.quantum-espresso.org<mailto:
> users at lists.quantum-espresso.org>
> https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso<
> http://www.max-centre.eu/quantum-espresso>)
> users mailing list users at lists.quantum-espresso.org<mailto:
> users at lists.quantum-espresso.org>
> https://lists.quantum-espresso.org/mailman/listinfo/users
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> ------------------------------
>
> Message: 7
> Date: Thu, 26 Sep 2019 21:57:25 +0200
> From: Paolo Giannozzi <p.giannozzi at gmail.com>
> To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
> Subject: Re: [QE-users] What Is Estimated SCF Accuracy
> Message-ID:
> <CAPMgbCssnkbb=
> vaGOR55DkuGkouV8wg6wYt8u2Vmrw_nCtznoA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> On Thu, Sep 26, 2019 at 9:44 PM Ben Comer <bcomer3 at gatech.edu> wrote:
>
> > Just a quick follow up, the text seems to imply that A7 is used rather
> > than A6. do you know where this is defined in the source code?
> >
> Variable dr2 in PW/src/mix_tho.f90, routine rho_ddot in PW/src/scf_mix.f90
>
> Paolo
>
> > On 9/26/19 10:57 AM, Paolo Giannozzi wrote:
> >
> > If I remember correctly: Eq.A6 of J.Phys.: Condens. Matter 21, 395502
> > (2009)
> >
> > Paolo
> >
> > On Thu, Sep 26, 2019 at 4:52 PM Ben Comer <bcomer3 at gatech.edu> wrote:
> >
> >> Hello,
> >>
> >> I'm trying to understand what exactly estimated SCF accuracy is. Does
> >> anyone know where I can find a formal definition of what it is and how
> >> it is being calculated? The structure of the output file implies that it
> >> is related to the Harris-Foulkes and the total energy, but it is clearly
> >> not the trivial difference between these two quantities.
> >>
> >> Thanks in advance,
> >> Ben Comer
> >> Georgia Tech
> >>
> >> _______________________________________________
> >> Quantum ESPRESSO is supported by MaX (
> www.max-centre.eu/quantum-espresso)
> >> users mailing list users at lists.quantum-espresso.org
> >> https://lists.quantum-espresso.org/mailman/listinfo/users
> >>
> >
> >
> > --
> > Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> > Phone +39-0432-558216, fax +39-0432-558222
> >
> >
> > _______________________________________________
> > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso
> )
> > users mailing list users at lists.quantum-espresso.orghttps://
> lists.quantum-espresso.org/mailman/listinfo/users
> >
> > _______________________________________________
> > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso
> )
> > users mailing list users at lists.quantum-espresso.org
> > https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
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> ------------------------------
>
> Message: 8
> Date: Fri, 27 Sep 2019 13:32:39 +0530
> From: Haider Abbas <haiderabbasphy at gmail.com>
> To: users at lists.quantum-espresso.org
> Subject: [QE-users] problems in graphene simulation
> Message-ID:
> <CAO+nntgthf6D0wOp2fPjg=wpfrndxK9=
> YrojmGeZFdc47UkjJw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear all,
>
> I am trying to simulate a modified structure of graphene. I have
> successfully obtained the desired results for band-structure and the
> bandgap match closely with the experimental value (2.7 eV). But I have some
> problems.
>
> 1- when I calculate the density of states with the combination of different
> k point, results are approximately the same, attached is the file.
> But the main problem is that the gap does not match with the bandgap,
> The density of states plot gives a gap of approx. 2 eV.
>
> 2- When I extract the PDOS, I have the contribution of 1S and 2P of carbon
> atoms and 1 S contribution of hydrogen atoms only.
> 2 S contribution of carbon is missing.
>
> with regards
>
> Haider Abbas
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