LAMMPS 单位制及其换算
LJ (Lennard-Jones) 单位制
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在 LJ 风格中，所有量都是无量纲的。LAMMPS 设定基本量：质量、σ、ε 和玻尔兹曼常数 kB = 1。所指定的质量、距离和能量都是这些基本值的倍数。
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时间单位关系式：τ = σ(m/ε)1/2
单位换算
| Reduced Quantity | Formula |
|---|---|
| Mass | m* = M/m |
| Distance | r* = r/σ |
| Time | t* = t/τ |
| Energy | E* = E/ε |
| Velocity | v* = vτ/σ |
| Force | f* = fσ/ε |
| Torque | t* = t/ε |
| Temperature | T* = TkB/ε |
| Pressure | p* = pσ3/ε |
| Dynamic Viscosity | η* = ησ3/ε |
| Charge | q* = q/√(4πε0εσ) |
| Dipole | μ* = μ/√(4πε0εσ3) |
| Electric Field | E* = E√(4πε0σ)/ε |
| Density | ρ* = ρσ3/m |
注：这些公式建立了约化或无量纲量（带星号）与其具有单位的物理量之间的关系。通过使用材料特定的质量、σ 和 ε 值，可以在无量纲 LJ 模拟结果和物理量之间进行转换。
real Units
| Property | Unit |
|---|---|
| mass | grams/mole |
| distance | Angstroms |
| time | femtoseconds |
| energy | kcal/mol |
| velocity | Angstroms/femtosecond |
| force | (kcal/mol)/Angstrom |
| torque | kcal/mol |
| temperature | Kelvin |
| pressure | atmospheres |
| dynamic viscosity | Poise |
| charge | multiple of electron charge (1.0 = proton) |
| dipole | charge×Angstroms |
| electric field | volts/Angstrom |
| density | g/cm^dim |
Metal Units
| Property | Unit |
|---|---|
| mass | grams/mole |
| distance | Angstroms |
| time | picoseconds |
| energy | eV |
| velocity | Angstroms/picosecond |
| force | eV/Angstrom |
| torque | eV |
| temperature | Kelvin |
| pressure | bars |
| dynamic viscosity | Poise |
| charge | multiple of electron charge (1.0 = proton) |
| dipole | charge×Angstroms |
| electric field | volts/Angstrom |
| density | gram/cm^dim |
SI Units
| Property | Unit |
|---|---|
| mass | kilograms |
| distance | meters |
| time | seconds |
| energy | Joules |
| velocity | meters/second |
| force | Newtons |
| torque | Newton-meters |
| temperature | Kelvin |
| pressure | Pascals |
| dynamic viscosity | Pascal×second |
| charge | Coulombs (1.6021765e-19 = proton) |
| dipole | Coulombs×meters |
| electric field | volts/meter |
| density | kilograms/meter^dim |
CGS Units
| Property | Unit |
|---|---|
| mass | grams |
| distance | centimeters |
| time | seconds |
| energy | ergs |
| velocity | centimeters/second |
| force | dynes |
| torque | dyne-centimeters |
| temperature | Kelvin |
| pressure | dyne/cm^2 (barye = 1.0e-6 bars) |
| dynamic viscosity | Poise |
| charge | statcoulombs/esu (4.8032044e-10 = proton) |
| dipole | statcoul-cm (10^18 debye) |
| electric field | statvolt/cm or dyne/esu |
| density | grams/cm^dim |
Electron Units
| Property | Unit |
|---|---|
| mass | atomic mass units |
| distance | Bohr |
| time | femtoseconds |
| energy | Hartrees |
| velocity | Bohr/atomic time units [1.03275e-15 seconds] |
| force | Hartrees/Bohr |
| temperature | Kelvin |
| pressure | Pascals |
| charge | multiple of electron charge (1.0 = proton) |
| dipole moment | Debye |
| electric field | volts/cm |
Micro Units
| Property | Unit |
|---|---|
| mass | picograms |
| distance | micrometers |
| time | microseconds |
| energy | picogram-micrometer^2/microsecond^2 |
| velocity | micrometers/microsecond |
| force | picogram-micrometer/microsecond^2 |
| torque | picogram-micrometer^2/microsecond^2 |
| temperature | Kelvin |
| pressure | picogram/(micrometer-microsecond^2) |
| dynamic viscosity | picogram/(micrometer-microsecond) |
| charge | picocoulombs (1.6021765e-7 = proton) |
| dipole | picocoulomb-micrometer |
| electric field | volt/micrometer |
| density | picograms/micrometer^dim |
Nano Units
| Property | Unit |
|---|---|
| mass | attograms |
| distance | nanometers |
| time | nanoseconds |
| energy | attogram-nanometer^2/nanosecond^2 |
| velocity | nanometers/nanosecond |
| force | attogram-nanometer/nanosecond^2 |
| torque | attogram-nanometer^2/nanosecond^2 |
| temperature | Kelvin |
| pressure | attogram/(nanometer-nanosecond^2) |
| dynamic viscosity | attogram/(nanometer-nanosecond) |
| charge | multiple of electron charge (1.0 = proton) |
| dipole | charge-nanometer |
| electric field | volt/nanometer |
| density | attograms/nanometer^dim |
Default Timestep and Skin Distance Values
| Style | Timestep (dt) | Skin Distance |
|---|---|---|
| lj | 0.005 τ | 0.3 σ |
| real | 1.0 femtoseconds | 2.0 Angstroms |
| metal | 0.001 picoseconds | 2.0 Angstroms |
| si | 1.0e-8 seconds | 0.001 meters |
| cgs | 1.0e-8 seconds | 0.1 centimeters |
| electron | 0.001 femtoseconds | 2.0 Bohr |
| micro | 2.0 microseconds | 0.1 micrometers |
| nano | 0.00045 nanoseconds | 0.1 nanometers |
