I run a TDA-BSE calculation for quasi-one-dimensional C60-fullerene-chain.
The quasi-one-dimensional C60-fullerene-chain is constructed by adjusting the distance (d) between two C60-fullerene-chains. When d is small, the system is considered as two-dimensional structure. For this two-dimensional structure, the TDA-BSE result seems to be fine. However, when d is large enough, the system is considered as quasi-one-dimensional C60-fullerene-chain. For this quasi-one-dimensional C60-fullerene-chain, the TDA-BSE calculation without scissor correction produces the negative excitonic transition energy. When the scissor correction (sc) is used, the TDA-BSE calculation does not produce the negative excitonic transition energy. I think the TDA-BSE is unstable, similar to viewtopic.php?t=1261
I try to analysize the TDA-BSE-sc results without negative excitonic transition energy, to my surprise, when I use ypp to analysize the first dark exciton (Es=0.27754515), the major IPA contribution (120_HOMO->121_LUMO) listed in the weights file shows that the IPA+sc transition energy (1.30) is much smaller than the smallest IPA transition energy output by pwscf+sc (1.27+0.84 = 2.118313).
Note that, the quasi-one-dimensional C60-fullerene-chain has a direct band gap.
I also tried to use the Coulomb potential cutoff and RIM, and got the similar results.
Some input and output files are attached. Any help will be appreciated.
Part of o-bse_k0205_blk5Ry_v10c15_X010.exc_qpt1_E_sorted
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# E [ev] Strength Index
#
0.27754515 0.87041714E-15 1.0000000
0.415798336 0.116360305E-6 2.00000000
0.489503205 0.178568413E-7 3.00000000
0.52257109 0.24699835E-15 4.0000000
0.59026492 0.91507294E-13 5.0000000
0.66519332 0.41979115E-11 6.0000000
0.707085669 0.723122503E-4 7.00000000
0.723453581 0.522076746E-7 8.00000000
1.0587963 0.72475255E-10 9.0000000
1.14108109 0.231848247E-6 10.0000000
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# E [ev] Strength Index
#
-0.56455517 0.13588325E-14 1.0000000
-0.426303297 0.116355196E-6 2.00000000
-0.352599204 0.178404331E-7 3.00000000
-0.31952795 0.59441336E-15 4.0000000
-0.25183672 0.40022032E-13 5.0000000
-0.17690800 0.41128806E-11 6.0000000
-0.135013938 0.723130215E-4 7.00000000
-0.118647352 0.522816563E-7 8.00000000
0.21669467 0.71330108E-10 9.0000000
0.298980176 0.231615005E-6 10.0000000
0.33745739 0.26135211E-09 11.000000
0.35067469 0.64098706E-14 12.000000
0.36473015 0.95327324E-09 13.000000
0.377417266 0.330991696E-6 14.0000000
0.41102618 0.64979502E-11 15.000000
0.432607919 0.127243638E-6 16.0000000
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# Band_V Band_C Kv-q ibz Symm_kv Kc q ibz Symm_kc Weight Energy [eV]
#
120 121 3 3 3 3 0.112998 1.305158
120 121 6 3 6 3 0.112985 1.305238
120 121 3 1 3 1 0.112871 1.305158
120 121 6 1 6 1 0.112858 1.305238