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{{TAGDEF|XC|PE | exchange-correlation functional in accordance with the {{FILE|POTCAR}} file}}
{{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 LDA, GGA exchange-correlation functional.
Description: Specifies a combination of exchange-correlation functionals.
----
----
This tag was added to perform GGA calculations with pseudopotentials generated with conventional LDA reference configurations.
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| important| VASP recalculates the exchange-correlation energy inside the PAW sphere and corrects the atomic energies given by the {{FILE|POTCAR}} file. For this to work, the original LEXCH tag must not be modified in the {{FILE|POTCAR}} file.}}
{{NB|mind|This tag is available since VASP.6.4.3.}}


A few points should be noted:
== Examples of {{FILE|INCAR}} ==
*The LIBXC option (or just LI) allows to use a LDA or GGA functional from the library of exchange-correlation functionals Libxc{{cite|marques:cpc:2012}}{{cite|lehtola:sx:2018}}{{cite|libxc}}. Along with {{TAG|GGA}}=LIBXC, it is also necessary to specify the {{TAG|LIBXC1}} and {{TAG|LIBXC2}} tags that specify the particular functional. Note that it is necessary to have [[Makefile.include#Libxc_.28optional.29|Libxc >= 5.2.0 installed]] and VASP.6.3.0 or higher compiled with [[Precompiler_options#-DUSELIBXC|precompiler options]].
*When the OR, BO, MK, ML or CX GGA is used in combination with the nonlocal vdW-DF functional of Dion ''et al.''{{cite|dion:prl:2004}}, the GGA component of the correlation should in principle be turned off with {{TAG|AGGAC}}=0 (see {{TAG|nonlocal vdW-DF functionals}}).
<!--
*The options in the last table allow to select range-separated ACFDT calculations, where a short-range local (DFT-like) exchange and correlation kernel is added to the long-range exchange and RPA correlation energy.
-->


The possible options for the {{TAG|GGA}} tag are:
*50% of PBE{{cite|perdew:prl:1996}} and 50% of PBEsol{{cite|perdew:prl:2008}}
<!--
{{TAG|XC}} = PE PS
:'''No functional:'''
  {{TAG|XC_C}} = 0.5 0.5
:{| border="1" cellspacing="0" cellpadding="5"
|-
|CO || No exchange-correlation
|-
|}
-->


*SCAN exchange{{cite|sun:prl:15}} combined with PBE correlation{{cite|perdew:prl:1996}}
{{TAG|XC}} = SCAN_X PBE_C
*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_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 ==
{{TAG|XC_C}},
{{TAG|GGA}},
{{TAG|METAGGA}}
{{TAG|LIBXC1}},
{{TAG|LIBXC1}},
{{TAG|LIBXC2}},
{{TAG|LIBXC2}},
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{{TAG|AGGAX}},
{{TAG|AGGAX}},
{{TAG|AGGAC}},
{{TAG|AGGAC}},
{{TAG|METAGGA}}
{{TAG|AMGGAX}},
{{TAG|AMGGAC}}


{{sc|GGA|Examples|Examples that use this tag}}
{{sc|XC|Examples|Examples that use this tag}}


== References ==
== References ==
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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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