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{{TAGDEF|XC|Combination of functionals}}
{{TAGDEF|XC|Combination of functionals}}
{{DEF|XC|{{TAG|GGA}}|if the {{TAG|GGA}} tag is used|{{TAG|METAGGA}}|if the {{TAG|METAGGA}} tag is used|The functional specified by {{TAG|LEXCH}} in the {{TAG|POTCAR}} file|if neither {{TAG|GGA}} nor {{TAG|METAGGA}} is used}}


Description: {{TAG|XC}} specifies a combination of exchange-correlation functionals.
Description: Specifies a combination of exchange-correlation functionals.
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A combination of semilocal functionals can be set with the {{TAG|XC}} tag. The functionals that can be combined are the functionals implemented in VASP (listed at {{TAG|GGA}} and {{TAG|METAGGA}}) and the functionals implemented in Libxc{{cite|marques:cpc:2012}}{{cite|lehtola:sx:2018}}{{cite|libxc}} (listed on the Libxc website{{cite|libxc_list}}). The combination can consist of up to 100 components; for each, a multiplication factor can be set with the {{TAG|XC_C}} tag.
A combination of semilocal (LDA, GGA, and METAGGA) functionals can be set with the {{TAG|XC}} tag, which provides much more flexibility in the choice of the functional compared to the {{TAG|GGA}} and {{TAG|METAGGA}} tags. The functionals that can be combined are the functionals implemented in VASP (listed at {{TAG|GGA}} and {{TAG|METAGGA}}) and the functionals implemented in Libxc{{cite|marques:cpc:2012}}{{cite|lehtola:sx:2018}}{{cite|libxc}} (listed on the Libxc website{{cite|libxc_list}}). The combination can consist of up to 100 components; for each, a multiplication factor can be set with the {{TAG|XC_C}} tag.
{{NB|mind|This tag is available since VASP.6.4.3.}}


== Examples of {{FILE|INCAR}} ==
== Examples of {{FILE|INCAR}} ==
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  {{TAG|XC_C}} = 0.5 0.5
  {{TAG|XC_C}} = 0.5 0.5


*SCAN exchange {{cite|perdew:prl:1996}} combined with PBE correlation{{cite|perdew:prl:1996}}
*SCAN exchange{{cite|sun:prl:15}} combined with PBE correlation{{cite|perdew:prl:1996}}
  {{TAG|XC}} = SCAN_X PBE_C
  {{TAG|XC}} = SCAN_X PBE_C


*70% of B88{{cite|becke:pra:1988}} (from Libxc) and 30% of PBE{{cite|perdew:prl:1996}} (from VASP) for exchange and 100% of LYP for correlation{{cite|lee:prb:1988}} (from Libxc)
*70% of B88{{cite|becke:pra:1988}} (from Libxc) and 30% of PBE{{cite|perdew:prl:1996}} for exchange and 100% of LYP (from Libxc) for correlation{{cite|lee:prb:1988}}  
  {{TAG|XC}} = GGA_X_B88 PBE_X GGA_C_LYP
  {{TAG|XC}} = GGA_X_B88 PBE_X GGA_C_LYP
  {{TAG|XC_C}} = 0.7 0.3 1.0
  {{TAG|XC_C}} = 0.7 0.3 1.0
*15% of HF, 63.75% of PBE{{cite|perdew:prl:1996}}, and 21.25% of B88{{cite|becke:pra:1988}} (from Libxc) for exchange and 75% of PBE{{cite|perdew:prl:1996}} and 25% of LYP{{cite|lee:prb:1988}} (from Libxc) for correlation
{{TAG|LHFCALC}} = .TRUE.
{{TAG|XC}}      = PE GGA_X_B88 GGA_C_LYP
{{TAG|XC_C}}    = 0.75 0.25 0.25
{{TAG|AEXX}}    = 0.15
{{TAG|AGGAX}}  = 0.85
:The PBE exchange is multiplied by <math>0.75\times0.85=0.6375</math> and the B88 exchange by <math>0.25\times0.85=0.2125</math>.
*15% of HF, 63.75% of PBE{{cite|perdew:prl:1996}}, and 21.25% of SCAN{{cite|sun:prl:15}} for exchange and 75% of PBE{{cite|perdew:prl:1996}} and 25% of SCAN{{cite|sun:prl:15}} for correlation
{{TAG|LHFCALC}} = .TRUE.
{{TAG|XC}}      = PE SCAN
{{TAG|XC_C}}    = 0.75 0.25
{{TAG|AEXX}}    = 0.15
{{TAG|AGGAX}}  = 0.85
{{TAG|AMGGAX}}  = 0.85
:The PBE exchange is multiplied by <math>0.75\times0.85=0.6375</math> and the SCAN exchange by <math>0.25\times0.85=0.2125</math>. {{TAG|AGGAX}} and {{TAG|AMGGAX}} multiply the exchange part of PBE and SCAN, respectively.


== Related tags and articles ==
== Related tags and articles ==
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<!--[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:GGA]][[Category:Meta-GGA]]-->
[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:GGA]][[Category:Meta-GGA]]

Latest revision as of 10:51, 19 March 2024

XC = Combination of functionals 

Default: XC = GGA if the GGA tag is used
= METAGGA if the METAGGA tag is used
= The functional specified by LEXCH in the POTCAR file if neither GGA nor METAGGA is used

Description: Specifies a combination of exchange-correlation functionals.

A combination of semilocal (LDA, GGA, and METAGGA) functionals can be set with the XC tag, which provides much more flexibility in the choice of the functional compared to the GGA and METAGGA tags. The functionals that can be combined are the functionals implemented in VASP (listed at GGA and METAGGA) and the functionals implemented in Libxc[1][2][3] (listed on the Libxc website[4]). The combination can consist of up to 100 components; for each, a multiplication factor can be set with the XC_C tag.

Mind: This tag is available since VASP.6.4.3.

Examples of INCAR

  • 50% of PBE[5] and 50% of PBEsol[6]
XC = PE PS
XC_C = 0.5 0.5
  • SCAN exchange[7] combined with PBE correlation[5]
XC = SCAN_X PBE_C
  • 70% of B88[8] (from Libxc) and 30% of PBE[5] for exchange and 100% of LYP (from Libxc) for correlation[9]
XC = GGA_X_B88 PBE_X GGA_C_LYP
XC_C = 0.7 0.3 1.0
  • 15% of HF, 63.75% of PBE[5], and 21.25% of B88[8] (from Libxc) for exchange and 75% of PBE[5] and 25% of LYP[9] (from Libxc) for correlation
LHFCALC = .TRUE.
XC      = PE GGA_X_B88 GGA_C_LYP
XC_C    = 0.75 0.25 0.25
AEXX    = 0.15
AGGAX   = 0.85
The PBE exchange is multiplied by and the B88 exchange by .
  • 15% of HF, 63.75% of PBE[5], and 21.25% of SCAN[7] for exchange and 75% of PBE[5] and 25% of SCAN[7] for correlation
LHFCALC = .TRUE.
XC      = PE SCAN
XC_C    = 0.75 0.25
AEXX    = 0.15
AGGAX   = 0.85
AMGGAX  = 0.85
The PBE exchange is multiplied by and the SCAN exchange by . AGGAX and AMGGAX multiply the exchange part of PBE and SCAN, respectively.

Related tags and articles

XC_C, GGA, METAGGA LIBXC1, LIBXC2, ALDAX, ALDAC, AGGAX, AGGAC, AMGGAX, AMGGAC

Examples that use this tag

References

  1. ↑ M. A. L. Marques, M. J. T. Oliveira, and T. Burnus, Comput. Phys. Commun., 183, 2272 (2012).
  2. ↑ S. Lehtola, C. Steigemann, M. J. T. Oliveira, and M. A. L. Marques, SoftwareX, 7, 1 (2018).
  3. ↑ https://libxc.gitlab.io
  4. ↑ https://libxc.gitlab.io/functionals/
  5. ↑ a b c d e f g J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett., 77, 3865 (1996).
  6. ↑ J. P. Perdew, A. Ruzsinszky, G. I. Csonka, O. A. Vydrov, G. E. Scuseria, L. A. Constantin, X. Zhou, and K. Burke, Phys. Rev. Lett. 100, 136406 (2008).
  7. ↑ a b c J. Sun, A. Ruzsinszky, and J. P. Perdew, Phys. Rev. Lett. 115, 036402 (2015).
  8. ↑ a b A. D. Becke, Density-functional exchange-energy approximation with correct asymptotic behavior, Phys. Rev. A 38, 3098 (1988).
  9. ↑ a b C. Lee, W. Yang, and R. G. Parr, Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density, Phys. Rev. B 37, 785 (1988).
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