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Add explanation for translation entropy constants #1077

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Add explanation for translation entropy constants #1077

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78bf7d4
Add explanation for translation entropy constants
TyBalduf Aug 6, 2024
8be94f9
Write out translational entropy terms more explicitly
TyBalduf Aug 8, 2024
b100421
Revert minor formatting changes
marcelmbn Aug 9, 2024
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13 changes: 12 additions & 1 deletion src/mctc/convert.f90
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Expand Up @@ -36,7 +36,7 @@ module xtb_mctc_convert
! convert Hartree (a.u.) to Joule and back
real(wp), public, parameter :: autoj = 4.3597447222071e-18_wp
real(wp), public, parameter :: jtoau = 1.0_wp / autoj
! convert Hartree to reciproce centimeters/wavenumbers and back
! convert Hartree to reciprocal centimeters/wavenumbers and back
real(wp), public, parameter :: autorcm = 219474.63067_wp
real(wp), public, parameter :: autowav = autorcm
real(wp), public, parameter :: rcmtoau = 1.0_wp / autorcm
Expand All @@ -63,6 +63,16 @@ module xtb_mctc_convert
! Debye to atomic units
real(wp), public, parameter :: autod = autoc * lightspeed * autoaa**2 * fstoau * 1.0e+16_wp
real(wp), public, parameter :: dtoau = 1.0_wp / autod
! Pressure
! atm -> Pascal
! au -> Pascal
! atm -> au
real(wp), public, parameter :: atmtopa = 101325.0_wp
real(wp), public, parameter :: patoatm = 1.0_wp / atmtopa
real(wp), public, parameter :: autopa = 2.9421015697e13_wp
real(wp), public, parameter :: patoau = 1.0_wp / autopa
real(wp), public, parameter :: atmtoau = atmtopa * patoau
real(wp), public, parameter :: autoatm = 1.0_wp / atmtoau

!> ----- DIPOLE DERIVATIVE UNITS -----
! Dipole derivatives along mass-weighted normal mode coordinates (a.u.) to km/mol (IR int.)
Expand Down Expand Up @@ -110,6 +120,7 @@ function m4bykgtoang4byamu() result(sitoang4byamu)
real(wp) :: sitoang4byamu
sitoang4byamu = (1.0e+10_wp)**4 / kgtoamu ! 16605390400000.0
end function m4bykgtoang4byamu

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!> ----------------------------------

end module xtb_mctc_convert
1 change: 0 additions & 1 deletion src/mctc/mctc_constants.f90
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Expand Up @@ -20,7 +20,6 @@ module xtb_mctc_constants
implicit none
private
real(wp),public,parameter :: pi = 3.1415926535897932384626433832795029_wp
real(wp),public,parameter :: pi4 = 3.1415926535897932384626433832795029_wp*4._wp
! √π
real(wp),public,parameter :: sqrtpi = sqrt(pi)
! 2×π
Expand Down
20 changes: 13 additions & 7 deletions src/thermo.f90
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Expand Up @@ -102,16 +102,18 @@ subroutine thermodyn(iunit,A_rcm,B_rcm,C_rcm,avmom_si,linear,atom,sym,molmass, &
logical, intent(in) :: linear !< is linear
logical, intent(in) :: atom !< only one atom
logical, intent(in) :: pr !< clutter the screen with printout
real(wp),parameter :: R = 1.98726D0 ! GAS CONSTANT IN CALORIES/MOLE
real(wp),parameter :: R = 1.98726D0 ! GAS CONSTANT IN CALORIES/(MOLE*K)
real(wp),parameter :: H = 6.626176D-27 ! PLANCK'S CONSTANT IN ERG-SECONDS
real(wp),parameter :: AK = 1.3807D-16 ! BOLTZMANN CONSTANT IN ERG/DEGREE
real(wp),parameter :: AK = 1.3807D-16 ! BOLTZMANN CONSTANT IN ERG/K
real(wp),parameter :: conv3 = amutokg*1000 ! 1.6606d-24
real(wp),parameter :: magic4 = 2.2868d0 ! unknown
real(wp),parameter :: magic5 = 2.3135d0 ! unknown
real(wp),parameter :: magic4 = 2.2868d0 ! R*ln(10)/2
real(wp),parameter :: magic5 = 2.3135d0 ! R*(ln[(kb/P°)*(2pi * kB * amutokg/h)^(3/2)] + 5/2)
! All terms in `magic5` in SI units (excluding R)
! P° corresponds to 1 atm in Pascals.
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real(wp),parameter :: caltoj = autokj/autokcal

integer :: i
real(wp) :: s_tr,s_rot,s_vib,s_int,s_tot
real(wp) :: s_tr,s_rot,s_vib,s_int,s_tot,s_tr_old
real(wp) :: h_tr,h_rot,h_vib,h_int,h_tot
real(wp) :: q_tr,q_rot,q_vib,q_int,q_tot
real(wp) :: cptr,cprot,cpvib,cpint,cptot
Expand All @@ -122,7 +124,7 @@ subroutine thermodyn(iunit,A_rcm,B_rcm,C_rcm,avmom_si,linear,atom,sym,molmass, &
real(wp) :: sv_ho,sv_rr
!*******************************************************************

! convert EVERYTHING to atomic units NOW and avoid horror and dispair later
! convert EVERYTHING to atomic units NOW and avoid horror and despair later
beta=1.0_wp/kB/T ! beta in 1/Eh
!c1=h*ac/ak/T ! beta in cm
sthr = sthr_rcm * rcmtoau ! sthr in Eh
Expand Down Expand Up @@ -219,7 +221,11 @@ subroutine thermodyn(iunit,A_rcm,B_rcm,C_rcm,avmom_si,linear,atom,sym,molmass, &
! this is 3/2rt+pv=5/2rt
h_tr=5.0_wp*R*T/2.0_wp
cptr=5.0_wp*R/2.0_wp
s_tr=magic4*(5.0_wp*log10(t)+3.0_wp*log10(molmass))-magic5
! Computed at standard pressure of 1 atm
s_tr_old=magic4*(5.0_wp*log10(t)+3.0_wp*log10(molmass))-magic5
s_tr=R*((2.5_wp*log(t*kB)&
& +1.5_wp*log(amutoau*molmass/(twopi))&
& -log(atmtoau) + 2.5_wp))
! *** CONSTRUCT TOTALS ***
cptot=cptr+cpint
s_tot=s_tr+s_int
Expand Down
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