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# Constants

Specifies 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.

#### 2010

Constants used in Gaussian 16, taken from [Mohr12, Mohr12a] and references therein. This is the default.

#### 2006

Constants used in Gaussian 09, taken from [Mohr08] and references therein.

#### 1998

Constants used in Gaussian 03 from [Mohr00] and references therein.

#### 1986

Constants used in Gaussian 88 through Gaussian 98, from [Cohen86, CRC80].

#### 1979

Constants used in Gaussian 80 through Gaussian 86, mostly from [Constyear79].

Here are summarized various conversion factors and physical constants used by Gaussian 16 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. Values without references are derived from the referenced quantities.

Raw Constants. The constants which are stored directly in the program are:

 1 Bohr (a0) = 0.52917721092 Å [Mohr12, Mohr12a] 1 Atomic mass unit (amu, mu) = 1.660538921 × 10-27 kilograms [Mohr12, Mohr12a] 1 Electron charge (e) = 1.602176565 × 10-19 Coulombs [Mohr12, Mohr12a] = 4.803204 × 10-10 ESU Planck's constant (h) = 6.62606957 × 10-34 Joule-secs [Mohr12, Mohr12a] Avogadro's number (NA) = 6.02214129 × 1023 [Mohr12, Mohr12a] 1 Kcal-mol-1 = 4.184 Joules-mol-1 [Constyear79] 1 Hartree(Eh) = 4.35974434 × 10-18 Joules [Mohr12, Mohr12a] Speed of light (c) = 2.99792458 × 1010 cm-sec-1 [Mohr12, Mohr12a] Boltzman constant (k) = 1.3806488 × 10-23 Joules-degree-1 [Mohr12, Mohr12a] Inverse fine structure constant (α-1) = 137.035999074 [Mohr12, Mohr12a] Molar volume of ideal gas at 273.15 K (Vm) = 0.022710953 m3 [Mohr12, Mohr12a] Proton rest mass (mp) = 1.672621777 × 10-27 kg [Mohr12, Mohr12a] Electron magnetic moment (μe) = -9.28476430 × 10-24 J T-1 [Mohr12, Mohr12a] Free electron g-factor (ge) = −2.00231930436153 (dimensionless) [Mohr12, Mohr12a]

Conversion Factors. The following useful conversion factors are included for your convenience:

 Electron mass (me) = 0.910938291 × 10-30 kg [Mohr12, Mohr12a] Proton mass (mp/me) = 1836.15267245 electron mass [Mohr12, Mohr12a] 1 Atomic mass unit (amu) = 1.660538921 × 10-27 kg [Mohr12, Mohr12a] = 1822.8885 electron mass 1 Electron volt (eV) = 1.602176565 × 10-19 Joules [Mohr12, Mohr12a] = 23.06 kcal-mol-1 1 Hartree = 627.5095 kcal-mol-1 = 27.2114 eV = 219474.63 cm-1 (vibrational freq. au) 1 Debye2-angstrom-2-amu-1 (IR intensity unit) = 42.2561 km-mol-1 = 5.82573 × 10-3 cm-2-atm-1 at STP Electric field: 1 au = 5.14220652 × 1011 V-m-1 [Mohr12, Mohr12a] Electric polarizability: 1 au = 1.6487772754 × 10-41 C2-m2-J-1 [Mohr12, Mohr12a] 1 Bohr-electron (electric dipole moment au) = 8.47835326 × 10-30 C-m [Mohr12, Mohr12a] = 2.541746 Debye = 2.541746 × 10-18 esu-cm