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The Atomic System of Units
Description
The atomic system is based on a unit of mass, the electron mass (approximately equal to kilograms), a unit of charge, the electron (approximately equal to coulombs), a unit of action, the planck (equal to Planck's constant over ), and a unit of electric permittivity written as kappa0 (equal to farads per meter, or one statfarad per centimeter, where is the magnitude of the speed of light).
By taking combinations of these four units, one can derive four units corresponding to the base dimensions length, mass, time, and electric current.
To facilitate using atomic units, enter the command Units[UseContext](Atomic) so that the second, volt, and tesla refer to the atomic and not SI context.
When used in conjunction with the UseSystem command, the atomic system sets the following units for the given dimensions. All units have context Atomic.
Dimension Name
Unit Name
mass
electron_mass
electric charge
electron
action
planck
electric permittivity
permittivity
length
bohr
time
second
force
hartree/bohr
energy
hartree
power
hartree per second
electric current
electron per second
electric potential
volt
electric capacitance
square electron per hartree
electric field strength
volt per bohr
electric displacement
electron per bohr squared
electric dipole moment
electron bohr
electric polarizability
electron bohr squared per volt
magnetic permeability
electron_mass bohr per electron squared
magnetic flux
volt second
magnetic flux density
tesla
magnetic inductance
volt second squared per electron
magnetizing force
hartree per tesla bohr cubed
hartree per tesla
magnetic polarizability
hartree per tesla squared
Atomic Base Units
All atomic base units have the context Atomic, including the second, where one atomic second is approximately SI second.
Unit Symbol
a0
em
s
electron/second
e/s
Atomic Derived Units with Special Names and Symbols
All units have the context Atomic.
Symbol
In Terms of Other Atomic Units
h_bar +
em*a0^2/s
E0
em*a0^2/s^2
kappa0
s^2*e^2/a0^3/em
electric potential difference
V
E0/e
T
em/s/e
A plus sign (+) indicates an abbreviation.
Examples
If infolevel is set to a greater integer (possible settings are 1 through 5), more detailed information about the computation method is displayed.
convert/system: "converting to the units e/a0^2"
convert/system: "converting to the units e^2/E0"
See Also
convert/system, convert/units, evalf, infolevel, Units, Units/Index, Units/Standard, Units/Systems, Units[UseSystem]
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