2020-09-17 23:44:25 +08:00
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!
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2020-12-17 06:10:07 +08:00
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! Copyright (C) 2020 Quantum ESPRESSO group
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2020-09-17 23:44:25 +08:00
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! This file is distributed under the terms of the
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! GNU General Public License. See the file `License'
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! in the root directory of the present distribution,
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! or http://www.gnu.org/copyleft/gpl.txt .
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!
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!----------------------------------------------------------------------------
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MODULE constants_l
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!----------------------------------------------------------------------------
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2020-11-27 01:18:08 +08:00
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!! A subset of the constants in 'Modules' folder of QE. Here the ones
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!! needed internally in xc_lib only.
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2020-09-17 23:44:25 +08:00
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!
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USE kind_l, ONLY : DP
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!
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IMPLICIT NONE
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!
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SAVE
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!
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! ... Mathematical constants
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!
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REAL(DP), PARAMETER :: pi = 3.14159265358979323846_DP
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REAL(DP), PARAMETER :: tpi = 2.0_DP * pi
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REAL(DP), PARAMETER :: fpi = 4.0_DP * pi
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REAL(DP), PARAMETER :: sqrtpi = 1.77245385090551602729_DP
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REAL(DP), PARAMETER :: sqrtpm1= 1.0_DP / sqrtpi
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REAL(DP), PARAMETER :: sqrt2 = 1.41421356237309504880_DP
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!
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!
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! ... Physical constants, atomic units:
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!
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REAL(DP), PARAMETER :: H_PLANCK_SI = 6.62607015E-34_DP ! J s
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REAL(DP), PARAMETER :: HARTREE_SI = 4.3597447222071E-18_DP ! J
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REAL(DP), PARAMETER :: BOHR_RADIUS_SI = 0.529177210903E-10_DP ! m
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REAL(DP), PARAMETER :: C_SI = 2.99792458E+8_DP ! m sec^-1
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!
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REAL(DP), PARAMETER :: AU_SEC = H_PLANCK_SI/tpi/HARTREE_SI
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!
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! Speed of light in atomic units
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REAL(DP), PARAMETER :: C_AU = C_SI / BOHR_RADIUS_SI * AU_SEC
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!
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! ... zero up to a given accuracy
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!
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REAL(DP), PARAMETER :: eps4 = 1.0E-4_DP
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REAL(DP), PARAMETER :: eps6 = 1.0E-6_DP
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REAL(DP), PARAMETER :: eps8 = 1.0E-8_DP
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REAL(DP), PARAMETER :: eps12 = 1.0E-12_DP
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REAL(DP), PARAMETER :: eps14 = 1.0E-14_DP
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REAL(DP), PARAMETER :: eps16 = 1.0E-16_DP
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REAL(DP), PARAMETER :: eps24 = 1.0E-24_DP
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REAL(DP), PARAMETER :: eps32 = 1.0E-32_DP
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!
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REAL(DP), PARAMETER :: gsmall = 1.0E-12_DP
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!
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REAL(DP), PARAMETER :: e2 = 2.0_DP ! the square of the electron charge
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!
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END MODULE constants_l
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