XCm_Pn
XCm_Pn = [real]
Description: XCm_Pn, where [math]\displaystyle{ m=1, 2, \ldots }[/math] and [math]\displaystyle{ n=1, 2, \ldots }[/math] allows to modify the parameters in a semilocal functional.
The XCm_Pn tag allows to modify the parameters in the semilocal functional set with the XC tag. In XCm_Pn, [math]\displaystyle{ m=1, 2, \ldots }[/math] refers to the [math]\displaystyle{ m }[/math]th component of the functional and [math]\displaystyle{ n=1, 2, \ldots }[/math] to the [math]\displaystyle{ n }[/math]th parameter of this [math]\displaystyle{ m }[/math]th functional component.
The XCm_Pn tag can be used for functionals that are implemented in VASP or in Libxc.
- Functionals in VASP:
- The number of functionals with modifiable parameters is for the moment very limited and concerns only a few MGGAs. Among the functionals listed at METAGGA, there is MS0, MS1, and MS2,[1][2] for instance. The functionals with modifiable parameters can be found by searching for "XC%PARAM" in the subroutine SET_XC_DATA in the setex.F file.
- Functionals in Libxc:
- For many of the functionals implemented in the library of exchange-correlation functionals Libxc[3][4][5] it is possible to modify the parameters. If a functional from Libxc has modifiable parameters, then they are listed in OUTCAR below "Parameters of Libxc functionals:" as P[math]\displaystyle{ n }[/math] ([math]\displaystyle{ n=1, 2, \ldots }[/math]). Note that LIBXC1_Pn and LIBXC2_Pn are equivalent to XCm_Pn when the functional is set with the tag GGA or METAGGA.
More information about the mixing and screening parameters in hybrid functionals can be found at LIBXC1_Pn.
| Mind: XCm_Pn is available since VASP.6.4.3. |
Examples
- In the GGA PBE functional,[6] as implemented in Libxc, the default parameters [math]\displaystyle{ \mu=0.21951 }[/math] in exchange and [math]\displaystyle{ \beta=0.066725 }[/math] in correlation are changed to [math]\displaystyle{ \mu=10/81\approx0.12345679 }[/math] and [math]\displaystyle{ \beta=0.046 }[/math] to get the PBEsol functional[7] (of course, the simpler way to use PBEsol from Libxc would be to call it directly with "XC=GGA_X_PBE_SOL GGA_C_PBE_SOL"). This example is equivalent to the one given for LIBXC1_Pn.
XC = GGA_X_PBE GGA_C_PBE XC1_P2 = 0.12345679 #parameter mu, which is the 2nd parameter in GGA_X_PBE XC2_P1 = 0.046 #parameter beta, which is the 1st parameter in GGA_C_PBE
- In the MGGA MS1 functional[2] the default parameters [math]\displaystyle{ \kappa=0.404 }[/math], [math]\displaystyle{ c=0.18150 }[/math] and [math]\displaystyle{ b=1.0 }[/math] in exchange are changed to [math]\displaystyle{ \kappa=0.504 }[/math], [math]\displaystyle{ c=0.14601 }[/math] and [math]\displaystyle{ b=4.0 }[/math] to get the MS2 functional.[2]
XC = MS1 XC1_P1 = 0.504 #parameter kappa, which is the 1st parameter in MS0, MS1, and MS2 XC1_P2 = 0.14601 #parameter c, which is the 2nd parameter in MS0, MS1, and MS2 XC1_P3 = 4 #parameter b, which is the 3rd parameter in MS0, MS1, and MS2
Related tags and articles
XC, XC_C, GGA, METAGGA, LIBXC1, LIBXC2, LIBXC1_Pn, LIBXC2_Pn
References
- ↑ J. Sun, B. Xiao, and A. Ruzsinszky, J. Chem. Phys. 137, 051101 (2012).
- ↑ a b c J. Sun, R. Haunschild, B. Xiao, I. W. Bulik, G. E. Scuseria, and J. P. Perdew, J. Chem. Phys. 138, 044113 (2013).
- ↑ M. A. L. Marques, M. J. T. Oliveira, and T. Burnus, Comput. Phys. Commun., 183, 2272 (2012).
- ↑ S. Lehtola, C. Steigemann, M. J. T. Oliveira, and M. A. L. Marques, SoftwareX, 7, 1 (2018).
- ↑ https://libxc.gitlab.io
- ↑ J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett., 77, 3865 (1996).
- ↑ 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).