Negative energy in exciton band structure including epc

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ymzhang
Posts: 5
Joined: Wed Jun 10, 2020 8:20 am

Negative energy in exciton band structure including epc

Post by ymzhang » Thu May 19, 2022 11:51 am

I want to interpolate hBN exciton band structure including electron-phonon coupling. However, I got negative energies on Q1 point as indicated by the tutorial website as:

Code: Select all

...
    -3.76358294        0.177910879E-4      219.000000         9.92491436
    -3.75403833        0.755890869E-4      215.000000         10.0377493
    -3.75096917        0.109721863E-3      207.000000         38.2221947
    -3.74093676        0.100141997E-4      209.000000         33.6967010
    -3.74088931        0.605661517E-4      208.000000         33.7033920
    -3.54611969        0.986570299         184.000000         22.9587269
    -3.54588223        0.309469014         185.000000         22.9632187
    -3.52316475        0.617848360E-3      186.000000         28.0695610
    -3.52294660        0.994357979E-3      187.000000         28.0626869
     3.52295780        0.517361797E-3      202.000000         28.0637016
     3.52316427        0.188250968E-3      203.000000         28.0689545
     3.54586959        0.268980145         201.000000         22.9626389
     3.54611135         1.00000000         200.000000         22.9591331
     3.74088335        0.640694489E-4      213.000000         33.7050209
     3.74091005        0.229923462E-4      212.000000         33.6954880
     3.75101256        0.107493564E-3      211.000000         38.2237701
     3.75404692        0.793393556E-4      210.000000         10.0376883
     3.76359320        0.722822460E-5      217.000000         9.92613029
...
Since the ypp only accept state range I think I can skip the negative energies and interpolated band 200-203, 210-213 separately. However, exciton energies is still negative on points other than Q1 and the interpolated bands are like:

Code: Select all

..

      0.185671568        0.514611781        -4.12325191        -2.75979447         5.65440512        0.120689653         0.00000000         0.00000000
      0.194513068        0.831551664E-2     -4.39890528        -3.12805891         5.57665730        0.126436785         0.00000000         0.00000000
      0.203354567       -0.544920862        -4.62475967        -3.47219968         5.47007990        0.132183909         0.00000000         0.00000000
      0.212196067        -1.14322174        -4.79626751        -3.78743505         5.33782244        0.137931034         0.00000000         0.00000000
      0.221037567        -1.78390229        -4.90914202        -4.06907082         5.18379450        0.143678159         0.00000000         0.00000000
      0.229879066        -2.46354914        -4.95943499        -4.31257296         5.01256466        0.149425283         0.00000000         0.00000000
      0.238720581        -3.17809415        -4.94363499        -4.51362991         4.82924604        0.155172423       -0.745058060E-8      0.00000000
      0.247562096        -3.92291451        -4.85873890        -4.66818857         4.63942480        0.160919562       -0.745058060E-8      0.00000000
      0.256403595        -4.69292021        -4.70233393        -4.77248192         4.44907951        0.166666672        0.745058060E-8      0.00000000
      0.265245110        -5.48265266        -4.47264099        -4.82302904         4.26454258        0.172413796         0.00000000         0.00000000
      0.274086624        -6.28635073        -4.16855574        -4.81662846         4.09246349        0.178160921        0.745058060E-8      0.00000000
      0.282928139        -7.09802675        -3.78966141        -4.75033188         3.93978453        0.183908060       -0.745058060E-8      0.00000000
      0.291769654        -7.91152954        -3.33623362        -4.62144041         3.81369758        0.189655170         0.00000000         0.00000000
      0.300611168        -8.72061920        -2.80921292        -4.42748451         3.72159219        0.195402309         0.00000000         0.00000000
      0.309452683        -9.51899338        -2.21022105        -4.16625500         3.67096305        0.201149434       -0.745058060E-8      0.00000000
      0.318294197        -10.3003855        -1.54151881        -3.83582401         3.66926694        0.206896558         0.00000000         0.00000000
      0.327135712        -11.0585966       -0.806048512        -3.43462825         3.72373629        0.212643683         0.00000000         0.00000000
      0.335977226        -11.7875948       -0.743483938E-2     -2.96156621         3.84113050        0.218390822         0.00000000         0.00000000
      0.344818741        -12.4815664        0.849942625        -2.41611862         4.02744198        0.224137947       -0.745058060E-8      0.00000000
...
Although I calculated the exciton eigenstates on 14 irreducible Q points. I can't get access to exciton energies on Q2 to Q14 using ypp_ph -e s. But I guess those negative energies appears due to the negative energy Q2 to Q14
How can I get rid of those unreasonable negative energies in finite temperature exciton band calculation.

Thanks
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claudio
Posts: 406
Joined: Tue Mar 31, 2009 11:33 pm
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Re: Negative energy in exciton band structure including epc

Post by claudio » Tue May 24, 2022 8:50 pm

Dear ymzhang

In order to include finite temperature effects in the BSE, one has to use the full BSE with "coupling":

http://www.yambo-code.org/wiki/index.ph ... on_solver)

This means that the BSE will contains both positive and negative energies,the anti-resonant part
viewtopic.php?t=2098

ignore the negative part and consider only the positive eigenvalues.
Claudio Attaccalite
[CNRS/ Aix-Marseille Université/ CINaM laborarory / TSN department
Campus de Luminy – Case 913
13288 MARSEILLE Cedex 09
web site: http://www.attaccalite.com

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