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Physical constant table (a shameless copy of Ben's collection)
electron charge e 1.602 176 53 x 10-19 C = 1/6.24150948E+18 C
electric constant \epsilon_o 8.854 187 817... x 10-12 F m-1 =8.854187817 x 10-12 C2/(N . m2) [or C2/(J.m)]
electric dipole 1 a.u. 8.47836 x 10-30 C-m, 1 D (the debye unit D ) = 3.336 x 10-30 Cm = 0.20822678 eA)
Avogadro constant N_A 6.022 1415 x 1023 mol-1
Boltzmann constant k 1.380 6505 x 10-23 J K-1
atomic mass constant m_u 1.660 538 86 x 10-27 kg
molar gas constant R 8.314 472 J mol-1 K-1
Planck constant h 6.626 0693 x 10-34 J s
Planck constant over 2 pi \bar h 1.054 571 68 x 10-34 J s
Faraday constant F 96 485.3383 C mol-1 = Na * e = 1.602E-19 * 6.022E+23
(capacitance, formula: A s V-1)
faraday (Fd): A unit of electric charge. The British electrochemist and physicist Michael Faraday (1791-1867) determined that the same amount of charge is needed to deposit one mole of any element. This amount of charge, equal to about 96 485 coulombs, became known as Faraday's constant. Later, it was adopted as a convenient unit for measuring the charges used in electrolysis. One faraday is equal to the product of Avogadro's number (see mole) and the charge (1 e) on a single electron.
concentration in molarity of standard state of water 55.5 M
(energy unit) cal 4.184 J
(concentration unit) M 1mol/liter = 1mol/cubic decimeter ~ (equivalent to) 1660.5 A3/molecule ~ 11.84 A/pair molecule distance, unit transform: 1M = 6.022 x 10-4 A-3

Units in equation
Poisson Equation · ε(r) φ(r,t) = ρ (r)
with possible boundary condition (as applied in biomolecular ele):
φ(r) = Q/(4*pi*ε*r)
or:
· ε(r) φ(r,t) = 4*pi*ρ (r)
with possible boundary condition (as applied in biomolecular ele):
φ(r) = Q/ ε*r

if using the finite difference or the finite element solving above partial differential equation, and take units \AA (length), e(charge), and relative dielectric constant\epsilon (unitless), then after obtaining the solution, the transformation of the potential \phi to unit kcal/mol/e is ( *4172.83 for the first eq, 332 for the second eq): ( the correct solution can not be obtained only through scaling the boundary values, but fixing the equation form)

Conversion Table Most of these numbers have been taken from an old book by Karplus and Porter. To convert from a unit Y in the left hand column to a unit X in the top row, mutiply by the table element, MX,Y. Example:
1 hartree = 27.2107 eV
When accuracy is very important, I recommend going instead to the NIST website: Fundamental Physical Constants from NIST
Energy Conversion Table

hartree eV cm-1 kcal/mol kJ/mol oK J Hz
hartree 1 27.2107 219 474.63 627.503 2 625.5 315 777. 43.60 x 10-19 6.57966 x 10+15
eV 0.0367502 1 8 065.73 23.060 9 96.486 9 11 604.9 1.602 10 x 10-19 2.418 04 x 10+14
cm-1 4.556 33 x 10-6 1.239 81 x 10-4 1 0.002 859 11 0.011 962 7 1.428 79 1.986 30 x 10-23 2.997 93 x 10+10
kcal/mol 0.001 593 62 0.043 363 4 349.757 1 4.18400 503.228 6.95 x 10-21 1.048 54 x 10+13
kJ/mol 0.000 380 88 0.010 364 10 83.593 0.239001 1 120.274 1.66 x 10-21 2.506 07 x 10+12
oK 0.000 003 166 78 0.000 086 170 5 0.695 028 0.001 987 17 0.008 314 35 1 1.380 54 x 10-23 2.083 64 x 10+10
J 2.294 x 10+17 6.241 81 x 10+18 5.034 45 x 10+22 1.44 x 10+20 6.02 x 10+20 7.243 54 x 10+22 1 1.509 30 x 10+33
Hz 1.519 83 x 10-16 4.135 58 x 10-15 3.335 65 x 10-11 9.537 02 x 10-14
4.799 30 x 10-11 6.625 61 x 10-34 1