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### pair_style awpmd/cut command

Syntax:

    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:

    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 wavepackets. 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 wavepackets. 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 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 command as in the examples above, or in the data file or restart files read by the read_data or 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 mix, shift, table, and tail options are not relevant for this pair style.

This pair style writes its information to binary restart files, 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 command. It does not support the inner, middle, outer keywords.

Restrictions: none

Related commands:

pair_coeff

Default:

These are the defaults for the pair_style keywords: hartree for the initial wavefunction, free for the wavepacket width.