111 lines
3.2 KiB
Fortran
111 lines
3.2 KiB
Fortran
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!=======================================================================
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!
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MODULE KINETIC_ENERGIES
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!
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USE ACCURACY_REAL
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!
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CONTAINS
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!
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!------ 1) 3D case --------------------------------------------
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!
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!=======================================================================
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!
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FUNCTION EK_3D(EK_TYPE,RS,T,XI)
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!
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! This subroutine computes the 3D kinetic energy EK
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! at a given value RS
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!
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!
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! Input parameters:
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!
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! * EK_TYPE : type of exchange energy functional
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! EK_TYPE = 'HEG' --> homogeneous electron gas
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! * IMODE : choice of parameters
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! IMODE = 1 : no spin polarization
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! IMODE = 2 : fully spin-polarized
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! * RS : Wigner-Seitz radius of electron (in units of a_0)
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! * T : temperature (SI)
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! * XI : spin polarization : (n+ - n-) / n
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!
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! Output parameters:
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!
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! * EK_3D : value at RS
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!
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!
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!
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! Author : D. Sébilleau
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!
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! Last modified : 15 Sep 2020
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!
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IMPLICIT NONE
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!
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CHARACTER (LEN = 3) :: EK_TYPE
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!
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REAL (WP), INTENT(IN) :: RS,T,XI
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REAL (WP) :: EK_3D
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!
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INTEGER :: IMODE
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!
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IF(EK_TYPE == 'HEG') THEN !
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EK_3D = EK_HEG_3D(RS,XI) !
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END IF !
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!
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END FUNCTION EK_3D
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!
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!=======================================================================
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!
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FUNCTION EK_HEG_3D(RS,XI)
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!
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! This function computes the kinetic energy in the 3D homegeneous
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! electron gas model
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!
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! Reference: (1) A. Sarkar, S. Haldar, D. Roy and D. Sen,
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! Acta Phys. Polonica A 106, 497-514 (2004)
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! (2) H. T. Tran and J. P. Perdew, Am. J. Phys. 71,
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! 1048-1061 (2003)
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!
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! Input parameters:
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!
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! * RS : Wigner-Seitz radius of electron (in units of a_0)
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! * XI : spin polarization : (n+ - n-) / n
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!
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! Output parameters:
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!
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! * EX_HEG : value at RS (in Ry)
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!
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!
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!
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! Author : D. Sébilleau
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!
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! Last modified : 15 Sep 2020
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!
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!
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USE REAL_NUMBERS, ONLY : ONE,TWO,THREE,FIVE,THIRD
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USE UTILITIES_1, ONLY : ALFA
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!
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IMPLICIT NONE
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!
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REAL (WP), INTENT(IN) :: RS,XI
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REAL (WP) :: EK_HEG_3D
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REAL (WP) :: ALPHA,COEF
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REAL (WP) :: A,E,FK
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REAL (WP) :: EK_P,EK_F
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!
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A = TWO**(TWO * THIRD) !
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E = FIVE * THIRD !
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FK = ( (ONE + XI)**E + (ONE - XI)**E - TWO ) / & !
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(TWO * (A - ONE) ) !
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!
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ALPHA = ALFA('3D') !
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COEF = THREE / (FIVE * ALPHA * ALPHA) ! ref. 2 eq. (4)
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EK_P = COEF / (RS * RS) !
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EK_F = A * EK_P !
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!
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EK_HEG_3D = EK_P + (EK_F - EK_P) * FK ! ref. 1 eq. (11)
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!
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END FUNCTION EK_HEG_3D
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!
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END MODULE KINETIC_ENERGIES
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