# ConstantsSpecifies
which set of physical constants to use. Note that using an older set should *only*
be done in order to compare results with earlier versions of *Gaussian*. **1998**
Constants from [428] and references therein. This
is the default
**1986** Constants used in *Gaussian 88 *through*
Gaussian 98*, from [429,430].
**1979**
Constants used in *Gaussian 80 *through* Gaussian 86*, mostly from [431].
The **OldConstants** keyword is a synonym for **Constants=1979**.
### CURRENT
VALUESHere are summarized various conversion factors and physical constants
used by *Gaussian 03* in converting from standard to atomic units. All quantities
used in calculations inside *Gaussian *are in atomic units; the conversion
factors are used only when processing input or generating printed output. **Raw
Constants**.** **The constants which are stored directly in the program are:
1
Bohr (*a*_{0}) = 0.5291772083 Å [428] 1
Atomic mass unit (amu) = 1.66053873 x 10^{-27} kilograms [428]
1 Electron charge (*e*) = 4.803242 x 10^{-10} ESU [432]
= 1.602176462 x 10^{-19} Coulombs [428] Planck's
constant (*h*) = 6.62606876 x 10^{-34} Joule-secs [428] Avogadro's
number (*N*_{A}) = 6.02214199 x 10^{23} [428] 1
Calorie = 4.184 Joules [431] 1 Hartree =
4.3597482 x 10^{-18} Joules [429] Speed
of light (*c*) = 2.99792458 x 10^{10} cm-sec^{-1} [431] Boltzman
constant (*k*) = 1.380603 x 10^{-23} Joules-degree^{-1} [428] Inverse
fine structure constant (α^{-1}) = 137.03599976 [428] Molar
volume of ideal gas at 273.15 K = 0.022413996 m^{3} [428] Proton
rest mass = 1.67262158 x 10^{-27} kg [428] Electron
magnetic moment = 9.28476362 x 10-^{24 }J-T^{-1 }[428] Free
electron g-factor = 2.002319304386 (dimensionless) [428] **Conversion
Factors**. The following useful conversion factors can be derived from the above:
Electron
mass = 0.910938 x 10^{-30} kg Proton mass = 1836.1527 electron mass
1 Atomic mass unit (amu) = 1822.8880 electron mass 1 Electron volt
(eV) = 23.06055 kcal-mol^{-1} 1 Hartree = 627.5095 kcal-mol^{-1}
= 27.2114 eV 1 Bohr-electron = 2.541746 Debye = 2.541746 x 10^{-18}
esu-cm 1 Debye^{2}-angstrom^{-2}-amu^{-1} = 42.2561
km-mol^{-1} = 5.82573 x 10^{-3} cm^{-2}-atm^{-1}
at STP 1 Hartree^{-1/2}-Bohr-1-amu^{-1/2} = 219474.6 cm^{-1} Electric
field: 1 au = 5.142206 x 10^{11 }V-m^{-1}
^{}Electric
polarizability: 1 au = 1.648777 x 10^{-41} C^{2}-m^{2}-J^{-1}
^{}Dipole moment = 1 Bohr-electron = 8.478352 x 10^{-30} C-m |