Updated and simplified documentation

min_modify keyword values ... :pre

one or more keyword/value pairs may be listed :ulb,l

keyword = {dmax} or {line} or {norm} or {alpha_damp} or {discrete_factor}

keyword = {dmax} or {line} or {norm} or {alpha_damp} or {discrete_factor} or {integrator} or {tmax}

  {dmax} value = max

    max = maximum distance for line search to move (distance units)

  {line} value = {backtrack} or {quadratic} or {forcezero} or {spin_cubic} or {spin_none}

  {alpha_damp} value = damping

    damping = fictitious Gilbert damping for spin minimization (adim)

  {discrete_factor} value = factor

    factor = discretization factor for adaptive spin timestep (adim) :pre

:ule

these keywords apply only to the "min_style"_min_style.html {fire2} :ulb,l

keyword = {integrator} or {tmax} or {tmin} or {delaystep} or {dtgrow} or {dtshrink} 

          or {alpha0} or {alphashrink} or {halfstepback} or {initialdelay} or {vdfmax}

  {integrator} arg = {eulerimplicit} or {eulerexplicit} or {verlet}

    eulerimplicit,eulerexplicit,verlet = integration scheme

  {tmax} arg = coef

    coef = factor defining the maximum timestep

  {tmin} arg = coef

    coef = factor defining the minimum timestep

  {delaystep} arg = delay

    delay = number of steps for dynamics delay

  {dtgrow} arg = grow

    grow = factor increasing the timestep

  {dtshrink} arg = shrink

    shrink = factor decreasing the timestep

  {alpha0} arg = alpha

    alpha = coefficient mixing velocities and forces

  {alphashrink} arg = shrink

    shrink = factor decreasing alpha

  {vdfmax} arg = max 

    max = maximum number of consecutive iterations with P(t) < 0 before forced interruption 

  {halfstepback} arg = {yes} or {no}

  {initialdelay} arg = {yes} or {no} :pre

    factor = discretization factor for adaptive spin timestep (adim)

  {integrator} value = {eulerimplicit} or {eulerexplicit} or {verlet}

    time integration scheme for fire2 minimization

  {tmax} value = factor

    factor = maximum adaptive timestep for fire2 minimization :pre

:ule

[Examples:]

min_modify dmax 0.2

min_modify integrator verlet tmax 0.4 :pre

min_modify integrator verlet tmax 4 :pre

[Description:]

and {spin/cg}. Convergence of {spin/lbfgs} can be more robust if

{spin_cubic} line search is used.

The style {fire2} has several parameters that can be tuned in order

to optimize the relaxation: {integrator}, {tmax}, {tmin}, {delaystep}, {dtgrow}, {dtshrink}, 

{alpha0}, and {alphashrink}.

Different Newton {integrator} can be selected: explicit Euler, 

semi-implicit Euler (= symplectic Euler) and velocity Verlet.

The parameters {tmax} and {tmin} define the maximum and minimum timestep 

allowed during an fire2 minimization. Those are not in time unit, but are 

multiplication factor applied to the "timestep"_timestep.html. Thus 

{tmax} = 10.0 in metal "units"_units.html means that the maximum value

the timestep can be reached during the relaxation is 10 fs (with the default

"timestep"_timestep.html value).

Note that even with the default parameters being chosen to be reliable in most

cases, adjusting "timestep"_timestep.html, {tmax} and {tmin} should be consider

to optimize the minimization, in particular for large/complex system.

The Newton {integrator} used for {fire2} minimization can be selected to be

either the symplectic Euler ({eulerimplicit}), explicit Euler (eulerexplicit)

or velocity Verlet ({verlet}). Note that explicit Euler is not recommended 

as it will lead to results similar to a {fire} minimization.

{tmax} define the maximum value for the adaptive timestep 

during a {fire2} minimization. It is multiplication factor applied 

to the current "timestep"_timestep.html (not in time unit). For example, 

{tmax} = 4.0 in metal "units"_units.html means that the maximum value

the timestep can reach during a minimization is 4fs (with the default

"timestep"_timestep.html value). Note that parameters defaults has been 

chosen to be reliable in most cases, but one should consider adjusting 

"timestep"_timestep.html and {tmax} to optimize the minimization for large 

or complex systems.

Others parameters of the {fire2} minimization can be tuned ({tmin}, {delaystep},

{dtgrow}, {dtshrink}, {alpha0}, and {alphashrink}). Please refer to the article

describing the {fire2} "min_style"_min_style.html.

An additional stopping criteria {vdfmax} is added in order to avoid unnecessary looping

when it is reasonable to think the system will not be relaxed further.

Note that in this case the system will NOT be relaxed. This could

of each atom is initialized to 0.0 by this style, at the beginning of

a minimization.

Style {fire2} is a re-implementation of the style {fire} with

additional optimizations of the method described

in "(Bitzek)"_#Bitzek, including different time integration schemes.

Style {fire2} is an optimization of the style {fire}, including different

time integration schemes, described in "(Guenole)"_#Guenole.

Style {spin} is a damped spin dynamics with an adaptive

timestep.

[(Bitzek)] Bitzek, Koskinen, Gahler, Moseler, Gumbsch, Phys Rev Lett,

97, 170201 (2006).

:link(Guenole)

[(Guenole)] Guenole, Nöhring, Vaid, Houllé, Xie, Prakash, Bitzek,

Preprint, arXiv:190802038 (2019).