made the command options more lammps standard style

fix ID group-ID neb Kspring keyword value :pre

ID, group-ID are documented in "fix"_fix.html command

neb = style name of this fix command

Kspring = parallel spring constant (force/distance units)

keyword = {idealpos} or {neigh} or {perp} or {freeend} :ul

 {idealpos} = each replica is attached with a spring to its interpolated ideal position (default)

 {neigh} = each replica is connected with spring to the previous and next replica.

 {perp} value = set spring constant for the perpendicular spring to {value}

 {freeend} flag = set behavior for the end points

   flag = {ini} or {final} or {finaleini} or {final2eini}

ID, group-ID are documented in "fix"_fix.html command :ulb,l

neb = style name of this fix command :l

Kspring = parallel spring constant (force/distance units or force units) :l

zero or more keyword/value pairs may be appended :l

keyword = {nudg_style} or {perp} or {freend} or {freend_k_spring} :l

  {nudg_style} value = {neigh} or {idealpos}

    {neigh} = the parallel nudging force is calculated from the distance to neighbouring replicas (in this case, Kspring is in force/distance units)

    {idealpos} = the parallel nudging force is proportional to the distance between the replica and its interpolated ideal position (in this case Kspring is in force units)

  {perp} value {none} or kspring2

    {none} = no perpendicular spring force is applied

  {freeend} value = {none} or {ini} or {final} or {finaleini} or {final2eini}

    {none} = no nudging force is apply to the first and last replicas

    {ini} = set the first replica to be a free end 

    {final} = set the last replica to be a free end

    {finaleini} = set the last replica to be a free end and set its target energy as that of the first replica

    {final2eini} = same as {finaleini} plus prevent intermediate replicas to have a lower energy than the first replica

  {freeend_kspring}  value = kspring2

    kspring2 = spring constant of the perpendicular spring force (per distance units)    

flag = set behavior for the end points

   flag = 

   :pre

[Examples:]

fix 1 active neb 10.0

fix 2 all neb 1.0 perp 1.0 freeend final

fix 1 all neb 1.0 neigh freeend final2eini :pre

fix 1 all neb 1.0 nudg_style idealpos freeend final2eini freend_kspring 1:pre

[Description:]

:line

The keywords {idealpos} and {neigh} allow to specify how to parallel

spring force is computed.  If the keyword {idealpos} is used or by

default, the spring force is computed as suggested in "(E)"_#E :

The keyword {nudg_style} allow to specify how to parallel

nudging force is computed. With a value of idealpos, the spring 

force is computed as suggested in "(E)"_#E :

Fspringparallel=-{Kspring}* (RD-RDideal)/(2 meanDist) :pre

Fnudgparallel=-{Kspring}* (RD-RDideal)/(2 meanDist) :pre

where RD is the "reaction coordinate" see "neb"_neb.html section, and

RDideal is the ideal RD for which all the images are equally spaced

is the replica number). The meanDist is the average distance between

replicas.

If the keyword {neigh} is used, the parallel spring force is computed

as in "(Henkelman1)"_#Henkelman1 by connecting each intermediate

replica with the previous and the next image:

When {nudg_style} has a value of neigh (or by default), the parallel 

nudging force is computed as in "(Henkelman1)"_#Henkelman1 by 

connecting each intermediate replica with the previous and the next 

image:

Fspringparallel= {Kspring}* (|Ri+1 - Ri| - |Ri - Ri-1|) :pre

Fnudgparallel= {Kspring}* (|Ri+1 - Ri| - |Ri - Ri-1|) :pre

The parallel spring force associated with the key word idealpos should

The parallel nudging force associated with the key word idealpos should

usually be more efficient at keeping the images equally spaced.

:line

[Default:]

none

The option defaults are nudg_style = neigh, perp = none, freeend = none and freend_kspring = 1.

:line

:link(Henkelman1)

[(Henkelman1)] Henkelman and Jonsson, J Chem Phys, 113, 9978-9985 (2000).

group		nonneb subtract all nebatoms

fix		1 lower setforce 0.0 0.0 0.0

fix		2 nebatoms neb 1.0 neigh

fix		2 nebatoms neb 1.0 nudg_style idealpos

fix		3 all enforce2d

thermo		100

group		nonneb subtract all nebatoms

fix		1 lower setforce 0.0 0.0 0.0

fix		2 nebatoms neb 1.0 freeend ini

fix		2 nebatoms neb 1.0 nudg_style idealpos freeend ini

fix		3 all enforce2d

thermo		100

group		nonneb subtract all nebatoms

fix		1 lower setforce 0.0 0.0 0.0

fix		2 nebatoms neb 1.0 neigh

fix		2 nebatoms neb 1.0 

fix		3 all enforce2d

thermo		100

reset_timestep	0

fix		1 all neb 1.0 neigh

fix		1 all neb 1.0 

thermo		100