[QE-users] dilectric constant

Lorenzo Paulatto paulatz at gmail.com
Mon Jun 3 09:08:13 CEST 2019


I think the issue is discussed in some detail in Phys. Rev. B 94, 085415 
this is implented in pw.x, ph.x, q2r and matdyn by setting 
assume_isolated="2D", see also the manual:


'2D' :

     Truncation of the Coulomb interaction in the z direction
     for structures periodic in the x-y plane. Total energy,
     forces and stresses are computed in a two-dimensional framework.
     Linear-response calculations () done on top of a self-consistent
     calculation with this flag will automatically be performed in
     the 2D framework as well. Please refer to:
     Sohier, T., Calandra, M., & Mauri, F. (2017), Density functional
     perturbation theory for gated two-dimensional heterostructures:
     Theoretical developments and application to flexural phonons in 
graphene.
     Physical Review B, 96(7), 75448. 
https://doi.org/10.1103/PhysRevB.96.075448

     NB:
        - The length of the unit-cell along the z direction should
          be larger than twice the thickness of the 2D material
          (including electrons). A reasonable estimate for a
          layer's thickness could be the interlayer distance in the
          corresponding layered bulk material. Otherwise,
          the atomic thickness + 10 bohr should be a safe estimate.
          There is also a lower limit of 20 bohr imposed by the cutoff
          radius used to read pseudopotentials (see read_pseudo.f90 in 
Modules).

        - As for ESM above, only in-plane stresses make sense and one
          should use cell_dofree='2Dxy' in a vc-relax calculation.




On 6/1/19 8:36 PM, Stefano Baroni wrote:
> ... of course, I meant “one”, not “zero” ... SB
> 
> ___
> Stefano Baroni, Trieste -- http://stefano.baroni.me
> 
> On 1 Jun 2019, at 13:17, Stefano Baroni <baroni at sissa.it 
> <mailto:baroni at sissa.it>> wrote:
> 
>> Not sure what you want to compute, but the dielectric constant of a 2D 
>> material is either zero or ill-defined, according to how you see it. 
>> Try for yourself what happens by doubling the interplanar spacing, 
>> which should not matter if you are interested in the properties of an 
>> isolated 2D sheet. SB
>>
>> --
>> Stefano Baroni, Trieste -- swift message written and sent on the go
>>
>> On 1 Jun 2019, at 12:53, Sabike Ghasemi <s.ghasemi at du.ac.ir 
>> <mailto:s.ghasemi at du.ac.ir>> wrote:
>>
>>> hi all,
>>> i did PHONONIC calculation and DYNMAT calculation for calculating of 
>>> dielectric constant of a 2d material. my out file is:
>>>
>>>
>>>      Program DYNMAT v.6.3MaX starts on  1Jun2019 at 20: 7:51
>>>
>>>      This program is part of the open-source Quantum ESPRESSO suite
>>>      for quantum simulation of materials; please cite
>>>          "P. Giannozzi et al., J. Phys.:Condens. Matter 21 395502 
>>> (2009 <callto:21 395502 (2009>);
>>>          "P. Giannozzi et al., J. Phys.:Condens. Matter 29 465901 
>>> (2017 <callto:29 465901 (2017>);
>>>           URL http://www.quantum-espresso.org",
>>>      in publications or presentations arising from this work. More 
>>> details at
>>> http://www.quantum-espresso.org/quote
>>>
>>>      Parallel version (MPI), running on     4 processors
>>>
>>>      MPI processes distributed on     1 nodes
>>>      R & G space division:  proc/nbgrp/npool/nimage =       4
>>>
>>>      Reading Dynamical Matrix from file ice.dynG
>>>      ...Force constants read
>>>      ...epsilon and Z* read
>>>      A direction for q was not specified:TO-LO splitting will be absent
>>>
>>>      Polarizability (A^3 units)
>>>      multiply by 0.957978 for Clausius-Mossotti correction
>>> 8.324588    0.005349 <callto:8.324588 0.005349>    0.014641
>>> 0.005349    8.319854 <callto:0.005349 8.319854>    0.008335
>>> 0.014643    0.008337 <callto:0.014643 0.008337>    4.733133
>>>
>>>      IR activities are in (D/A)^2/amu units
>>>
>>> # mode   [cm-1]    [THz]      IR
>>> 1     68.10    2.0416 <callto:1 68.10 2.0416>    0.0390
>>> 2     92.11    2.7615 <callto:2 92.11 2.7615>    0.0437
>>> 3    105.83    3.1728 <callto:3 105.83 3.1728>    0.0170
>>> 4    118.67    3.5575 <callto:4 118.67 3.5575>    0.0073
>>> 5    143.19    4.2926 <callto:5 143.19 4.2926>    0.0184
>>> 6    174.06    5.2181 <callto:6 174.06 5.2181>    0.0166
>>> 7    188.29    5.6449 <callto:7 188.29 5.6449>    0.0220
>>> 8    197.18    5.9112 <callto:8 197.18 5.9112>    0.0728
>>> 9    210.77    6.3186 <callto:9 210.77 6.3186>    0.1032
>>> 10    222.12    6.6589 <callto:10 222.12 6.6589>    0.1143
>>> 11    242.57    7.2720 <callto:11 242.57 7.2720>    0.0639
>>> 12    259.72    7.7863 <callto:12 259.72 7.7863>    0.6321
>>> 13    284.43    8.5270 <callto:13 284.43 8.5270>    0.0361
>>> 14    344.19   10.3186 <callto:14 344.19 10.3186>    0.1235
>>> 15    349.74   10.4849 <callto:15 349.74 10.4849>    0.2905
>>> 16    401.58   12.0390 <callto:16 401.58 12.0390>    0.2049
>>> 17    459.16   13.7654 <callto:17 459.16 13.7654>    3.0010
>>> 18    485.68   14.5603 <callto:18 485.68 14.5603>    0.1163
>>> 19    512.01   15.3497 <callto:19 512.01 15.3497>    7.3524
>>> 20    547.15   16.4031 <callto:20 547.15 16.4031>    0.0176
>>> 21    572.56   17.1649 <callto:21 572.56 17.1649>    1.6482
>>> 22    578.65   17.3474 <callto:22 578.65 17.3474>    3.4530
>>> 23    655.06   19.6383 <callto:23 655.06 19.6383>    0.0721
>>> 24    669.05   20.0576 <callto:24 669.05 20.0576>    8.1208
>>> 25   1615.69   48.4370 <callto:25 1615.69 48.4370>    3.8476
>>> 26   1618.08   48.5088 <callto:26 1618.08 48.5088>    1.0009
>>> 27   1621.49   48.6109 <callto:27 1621.49 48.6109>    2.5108
>>> 28   1702.50   51.0397 <callto:28 1702.50 51.0397>    0.0050
>>> 29   3538.51  106.0819 <callto:29 3538.51 106.0819>    9.6552
>>> 30   3553.03  106.5171 <callto:30 3553.03 106.5171>   22.1032
>>> 31   3594.79  107.7691 <callto:31 3594.79 107.7691>    3.9027
>>> 32   3606.19  108.1109 <callto:32 3606.19 108.1109>    0.7098
>>> 33   3678.64  110.2830 <callto:33 3678.64 110.2830>    0.1321
>>> 34   3690.93  110.6514 <callto:34 3690.93 110.6514>    4.7531
>>> 35   3694.76  110.7662 <callto:35 3694.76 110.7662>   17.1649
>>> 36   3712.49  111.2976 <callto:36 3712.49 111.2976>    7.8939
>>>
>>> Electronic dielectric permittivity tensor (F/m units)
>>> 1.153734    0.000099 <callto:1.153734 0.000099>    0.000270
>>> 0.000099    1.153647 <callto:0.000099 1.153647>    0.000154
>>> 0.000270    0.000154 <callto:0.000270 0.000154>    1.087409
>>>
>>>  ... with zone-center polar mode contributions
>>> 1.319859    0.006043 <callto:1.319859 0.006043>    0.059567
>>> 0.006043    1.280091 <callto:0.006043 1.280091>    0.002674
>>> 0.059567    0.002674 <callto:0.059567 0.002674>    1.183898
>>>
>>>
>>>      DYNMAT       :     0.08s CPU         0.12s WALL
>>>
>>>
>>>    This run was terminated on:  20: 7:51   1Jun2019
>>>
>>> =------------------------------------------------------------------------------=
>>>    JOB DONE.
>>> =------------------------------------------------------------------------------=
>>>
>>>
>>>
>>> in my out file two dielectric tansors are calculated. the first is 
>>> electronic part(infinite dielectric constant) and the second is total 
>>> part(ionic and electronic partition).
>>> however,my question : why is non-diagonal elements nonzero?
>>>  is my calculation wrong?
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> 
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-- 
Lorenzo Paulatto - Paris


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