# pair_style awpmd/cut command

## Syntax

``` LAMMPS
pair_style awpmd/cut Rc keyword value ...
```

-   Rc = global cutoff, -1 means cutoff of half the shortest box length

-   zero or more keyword/value pairs may be appended

-   keyword = *hartree* or *dproduct* or *uhf* or *free* or *pbc* or
    *fix* or *harm* or *ermscale* or *flex_press*

        *hartree* value = none
        *dproduct* value = none
        *uhf* value = none
        *free* value = none
        *pbc* value = Plen
          Plen = periodic width of electron = -1 or positive value (distance units)
        *fix* value = Flen
          Flen = fixed width of electron = -1 or positive value (distance units)
        *harm* value = width
          width = harmonic width constraint
        *ermscale* value = factor
          factor = scaling between electron mass and width variable mass
        *flex_press* value = none

## Examples

``` LAMMPS
pair_style awpmd/cut -1
pair_style awpmd/cut 40.0 uhf free
pair_coeff * *
pair_coeff 2 2 20.0
```

## Description

This pair style contains an implementation of the Antisymmetrized Wave
Packet Molecular Dynamics (AWPMD) method. Need citation here. Need basic
formulas here. Could be links to other documents.

Rc is the cutoff.

The pair_style command allows for several optional keywords to be
specified.

The *hartree*, *dproduct*, and *uhf* keywords specify the form of the
initial trial wave function for the system. If the *hartree* keyword is
used, then a Hartree multielectron trial wave function is used. If the
*dproduct* keyword is used, then a trial function which is a product of
two determinants for each spin type is used. If the *uhf* keyword is
used, then an unrestricted Hartree-Fock trial wave function is used.

The *free*, *pbc*, and *fix* keywords specify a width constraint on the
electron wave packets. If the *free* keyword is specified, then there is
no constraint. If the *pbc* keyword is used and *Plen* is specified as
-1, then the maximum width is half the shortest box length. If *Plen* is
a positive value, then the value is the maximum width. If the *fix*
keyword is used and *Flen* is specified as -1, then electrons have a
constant width that is read from the data file. If *Flen* is a positive
value, then the constant width for all electrons is set to *Flen*.

The *harm* keyword allow oscillations in the width of the electron wave
packets. More details are needed.

The *ermscale* keyword specifies a unitless scaling factor between the
electron masses and the width variable mass. More details needed.

If the *flex_press* keyword is used, then a contribution from the
electrons is added to the total virial and pressure of the system.

This potential is designed to be used with [atom_style
wavepacket](atom_style) definitions, in order to handle the description
of systems with interacting nuclei and explicit electrons.

The following coefficients must be defined for each pair of atoms types
via the [pair_coeff](pair_coeff) command as in the examples above, or in
the data file or restart files read by the [read_data](read_data) or
[read_restart](read_restart) commands, or by mixing as described below:

-   cutoff (distance units)

For *awpmd/cut*, the cutoff coefficient is optional. If it is not used
(as in some of the examples above), the default global value specified
in the pair_style command is used.

------------------------------------------------------------------------

## Mixing, shift, table, tail correction, restart, rRESPA info

The [pair_modify](pair_modify) mix, shift, table, and tail options are
not relevant for this pair style.

This pair style writes its information to [binary restart
files](restart), so pair_style and pair_coeff commands do not need to be
specified in an input script that reads a restart file.

This pair style can only be used via the *pair* keyword of the
[run_style respa](run_style) command. It does not support the *inner*,
*middle*, *outer* keywords.

------------------------------------------------------------------------

## Restrictions

> none

## Related commands

[pair_coeff](pair_coeff)

## Default

These are the defaults for the pair_style keywords: *hartree* for the
initial wave function, *free* for the wave packet width.