diff --git a/doc/pair_eff.html b/doc/pair_eff.html index a2aaa1a882..5e287f066e 100644 --- a/doc/pair_eff.html +++ b/doc/pair_eff.html @@ -13,25 +13,33 @@

Syntax:

-

pair_style eff/cut cutoff eradius_limit_flag pressure_flag +

pair_style eff/cut cutoff limit_eradius pressure_with_evirials ecp type1 element1 type2 element2 ... typeN elementN +

+

cutoff = global cutoff for Coulombic interactions +limit_eradius = limit electron size (optional) +pressure_with_evirials = include electron virials in system pressure (optional) +type1 ... typeN = lammps atom type +element1 ... element2 = element symbol : ul

-

Examples:

-
pair_style eff/cut 39.7
-pair_style eff/cut 40.0 1 1
+
pair_style eff/cut 39.7
+pair_style eff/cut 40.0 limit_eradius
+pair_style eff/cut 40.0 limit_eradius pressure_with_evirials
+pair_style eff/cut 40.0 ecp 1 Si 3 C
 pair_coeff * *
-pair_coeff 2 2 20.0 
-
+pair_coeff 2 2 20.0 +pair_coeff 1 s 0.320852 2.283269 0.814857 +pair_coeff 3 22.721015 0.728733 1.103199 17.695345 6.693621 : pre +

Description:

This pair style contains a LAMMPS implementation of the electron Force Field (eFF) potential currently under development at Caltech, as -described in (Jaramillo-Botero). The eFF was -first introduced by (Su) in 2007. +described in (Jaramillo-Botero). The eFF for Z<6 was +first introduced by (Su) in 2007. It has been extended to higher Zs +by using effective core potentials (ECPs) that now cover up to 2nd and 3rd +row p-block elements of the periodic table.

eFF can be viewed as an approximation to QM wave packet dynamics and Fermionic molecular dynamics, combining the ability of electronic @@ -138,25 +146,36 @@ individual I,J type pair via the pair_coeff comm All type pairs use the same global cutoff specified in the pair_style command.

-

The eradius_limit_flag and pressure_flag settings are optional. -Neither or both must be specified. If not specified they are -both set to 0 by default. +

The limit_eradius and pressure_with_evirials settings are optional. +Neither or both must be specified. If not specified they are unset.

-

The eradius_limit_flag is used to restrain electrons from becoming -unbounded in size at very high temperatures were the Gaussian wave +

The limit_eradius is used to restrain electron size from becoming +excessively diffuse at very high temperatures were the Gaussian wave packet representation breaks down, and from expanding as free -particles to infinite size. A setting of 0 means do not impose this -restraint. A setting of 1 imposes the restraint. The restraining -harmonic potential takes the form E = 1/2k_ss^2 for s > L_box/2, where -k_s = 1 Hartrees/Bohr^2. +particles to infinite size. If unset, electron radius is free to +increase without bounds. If set, a restraining +harmonic potential of the form E = 1/2k_ss^2 for s > L_box/2, where +k_s = 1 Hartrees/Bohr^2, is applied on the electron radius.

-

The pressure_flag is used to control between two types of pressure -computation: if set to 0, the computed pressure does not include the +

The pressure_with_evirials is used to control between two types of pressure +computation: if unset, the computed pressure does not include the electronic radial virials contributions to the total pressure (scalar -or tensor). If set to 1, the computed pressure will include the +or tensor). If set, the computed pressure will include the electronic radial virial contributions to the total pressure (scalar and tensor).

+

The ecp is used to associate an ECP representation for a particular atom type. +The ECP captures the orbital overlap between a core pseudo particle and valence electrons +within the Pauli repulsion. A list of type:element-symbol pairs may be provided for all +ECP representations, after the "ecp" keyword. +

+

IMPORTANT NOTE: Default ECP parameters are provided for C, N, O, Al, and Si. +Users can modify these using the pair_coeff command as exemplified above. +For this, the User must distinguish between two different functional forms supported, +one that captures the orbital overlap assuming the s-type core interacts with an s-like valence electron (s-s) +and another that assumes the interaction is s-p. For systems that exhibit significant p-character (e.g. C, N, O) +the s-p form is recommended. The "s" ECP form requires 3 parameters and the "p" 5 parameters. +

IMPORTANT NOTE: there are two different pressures that can be reported for eFF when defining this pair_style, one (default) that considers electrons do not contribute radial virial components (i.e. electrons @@ -171,26 +190,25 @@ partitioning changes, the total energy remains similar).

-

IMPORTANT NOTE: The currently implemented eFF gives a reasonably -accurate description for systems containing nuclei from Z = 1-6. -Users interested in applying eFF should restrict to systems where -electrons are s-like, or contain p character only insofar as a single -lobe of electron density is shifted away from the nuclear center. See -further details about some of the virtues and current limitations of -the method in (Jaramillo-Botero). +

IMPORTANT NOTE: This implemention of eFF gives a reasonably +accurate description for systems containing nuclei from Z = 1-6 in "all electron" representations. +For systems with increasingly non-spherical electrons, Users should use the ECP representations. +ECPs are now supported and validated for most of the 2nd and 3rd row elements of the p-block. +Predefined parameters are provided for C, N, O, Al, and Si. The ECP captures the orbital overlap +between the core and valence electrons (i.e. Pauli repulsion) with one of the functional forms:

-

Work is underway to extend the eFF to higher Z elements with -increasingly non-spherical electrons (p-block and d-block), to provide -explicit terms for electron correlation/exchange, and to improve its -computational efficiency via atom models with fixed 2 s core electrons -and atom models represented as pseudo-cores plus valence electrons. +

+
+
+
+

Where the 1st form correspond to core interactions with s-type valence electrons +and the 2nd to core interactions with p-type valence electrons.

-

The current version adds support for models with fixed-core and -effective pseudo-core (i.e. effective core pseudopotentials, ECP) +

The current version adds full support for models with fixed-core and ECP definitions. to enable larger timesteps (i.e. by avoiding the high frequency vibrational modes -translational and radial- of the 2 s -electrons), and in the ECP case to reduce the p-character effects in -higher Z elements (e.g. Silicon). A fixed-core should be defined with +electrons), and in the ECP case to reduce the increased orbital complexity in higher Z elements (up to Z<18). +A fixed-core should be defined with a mass that includes the corresponding nuclear mass plus the 2 s electrons in atomic mass units (2x5.4857990943e-4), and a radius equivalent to that of minimized 1s electrons (see examples under @@ -271,7 +289,7 @@ atoms.

Default:

-

If not specified, eradius_limit_flag = 0 and pressure_flag = 0. +

If not specified, limit_eradius = 0 and pressure_with_evirials = 0.

diff --git a/doc/pair_eff.txt b/doc/pair_eff.txt index 7e38770102..c79afef59f 100644 --- a/doc/pair_eff.txt +++ b/doc/pair_eff.txt @@ -10,25 +10,33 @@ pair_style eff/cut command :h3 [Syntax:] -pair_style eff/cut cutoff eradius_limit_flag pressure_flag +pair_style eff/cut cutoff limit_eradius pressure_with_evirials ecp type1 element1 type2 element2 ... typeN elementN cutoff = global cutoff for Coulombic interactions -eradius_limit_flag = 0 or 1 for whether electron size is restrained (optional) -pressure_flag = 0 or 1 to define the type of pressure calculation (optional) :ul +limit_eradius = limit electron size (optional) +pressure_with_evirials = include electron virials in system pressure (optional) +type1 ... typeN = lammps atom type +element1 ... element2 = element symbol : ul [Examples:] pair_style eff/cut 39.7 -pair_style eff/cut 40.0 1 1 +pair_style eff/cut 40.0 limit_eradius +pair_style eff/cut 40.0 limit_eradius pressure_with_evirials +pair_style eff/cut 40.0 ecp 1 Si 3 C pair_coeff * * -pair_coeff 2 2 20.0 :pre +pair_coeff 2 2 20.0 +pair_coeff 1 s 0.320852 2.283269 0.814857 +pair_coeff 3 22.721015 0.728733 1.103199 17.695345 6.693621 : pre [Description:] This pair style contains a LAMMPS implementation of the electron Force Field (eFF) potential currently under development at Caltech, as -described in "(Jaramillo-Botero)"_#Jaramillo-Botero. The eFF was -first introduced by "(Su)"_#Su in 2007. +described in "(Jaramillo-Botero)"_#Jaramillo-Botero. The eFF for Z<6 was +first introduced by "(Su)"_#Su in 2007. It has been extended to higher Zs +by using effective core potentials (ECPs) that now cover up to 2nd and 3rd +row p-block elements of the periodic table. eFF can be viewed as an approximation to QM wave packet dynamics and Fermionic molecular dynamics, combining the ability of electronic @@ -135,25 +143,36 @@ individual I,J type pair via the "pair_coeff"_pair_coeff.html command. All type pairs use the same global cutoff specified in the pair_style command. -The {eradius_limit_flag} and {pressure_flag} settings are optional. -Neither or both must be specified. If not specified they are -both set to 0 by default. +The {limit_eradius} and {pressure_with_evirials} settings are optional. +Neither or both must be specified. If not specified they are unset. -The {eradius_limit_flag} is used to restrain electrons from becoming -unbounded in size at very high temperatures were the Gaussian wave +The {limit_eradius} is used to restrain electron size from becoming +excessively diffuse at very high temperatures were the Gaussian wave packet representation breaks down, and from expanding as free -particles to infinite size. A setting of 0 means do not impose this -restraint. A setting of 1 imposes the restraint. The restraining -harmonic potential takes the form E = 1/2k_ss^2 for s > L_box/2, where -k_s = 1 Hartrees/Bohr^2. +particles to infinite size. If unset, electron radius is free to +increase without bounds. If set, a restraining +harmonic potential of the form E = 1/2k_ss^2 for s > L_box/2, where +k_s = 1 Hartrees/Bohr^2, is applied on the electron radius. -The {pressure_flag} is used to control between two types of pressure -computation: if set to 0, the computed pressure does not include the +The {pressure_with_evirials} is used to control between two types of pressure +computation: if unset, the computed pressure does not include the electronic radial virials contributions to the total pressure (scalar -or tensor). If set to 1, the computed pressure will include the +or tensor). If set, the computed pressure will include the electronic radial virial contributions to the total pressure (scalar and tensor). +The {ecp} is used to associate an ECP representation for a particular atom type. +The ECP captures the orbital overlap between a core pseudo particle and valence electrons +within the Pauli repulsion. A list of type:element-symbol pairs may be provided for all +ECP representations, after the "ecp" keyword. + +IMPORTANT NOTE: Default ECP parameters are provided for C, N, O, Al, and Si. +Users can modify these using the {pair_coeff} command as exemplified above. +For this, the User must distinguish between two different functional forms supported, +one that captures the orbital overlap assuming the s-type core interacts with an s-like valence electron (s-s) +and another that assumes the interaction is s-p. For systems that exhibit significant p-character (e.g. C, N, O) +the s-p form is recommended. The "s" ECP form requires 3 parameters and the "p" 5 parameters. + IMPORTANT NOTE: there are two different pressures that can be reported for eFF when defining this pair_style, one (default) that considers electrons do not contribute radial virial components (i.e. electrons @@ -168,26 +187,24 @@ partitioning changes, the total energy remains similar). :line -IMPORTANT NOTE: The currently implemented eFF gives a reasonably -accurate description for systems containing nuclei from Z = 1-6. -Users interested in applying eFF should restrict to systems where -electrons are s-like, or contain p character only insofar as a single -lobe of electron density is shifted away from the nuclear center. See -further details about some of the virtues and current limitations of -the method in "(Jaramillo-Botero)"_#Jaramillo-Botero. +IMPORTANT NOTE: This implemention of eFF gives a reasonably +accurate description for systems containing nuclei from Z = 1-6 in "all electron" representations. +For systems with increasingly non-spherical electrons, Users should use the ECP representations. +ECPs are now supported and validated for most of the 2nd and 3rd row elements of the p-block. +Predefined parameters are provided for C, N, O, Al, and Si. The ECP captures the orbital overlap +between the core and valence electrons (i.e. Pauli repulsion) with one of the functional forms: -Work is underway to extend the eFF to higher Z elements with -increasingly non-spherical electrons (p-block and d-block), to provide -explicit terms for electron correlation/exchange, and to improve its -computational efficiency via atom models with fixed 2 s core electrons -and atom models represented as pseudo-cores plus valence electrons. +:c,image(Eqs/eff_ECP1.jpg) +:c,image(Eqs/eff_ECP2.jpg) -The current version adds support for models with fixed-core and -effective pseudo-core (i.e. effective core pseudopotentials, ECP) +Where the 1st form correspond to core interactions with s-type valence electrons +and the 2nd to core interactions with p-type valence electrons. + +The current version adds full support for models with fixed-core and ECP definitions. to enable larger timesteps (i.e. by avoiding the high frequency vibrational modes -translational and radial- of the 2 s -electrons), and in the ECP case to reduce the p-character effects in -higher Z elements (e.g. Silicon). A fixed-core should be defined with +electrons), and in the ECP case to reduce the increased orbital complexity in higher Z elements (up to Z<18). +A fixed-core should be defined with a mass that includes the corresponding nuclear mass plus the 2 s electrons in atomic mass units (2x5.4857990943e-4), and a radius equivalent to that of minimized 1s electrons (see examples under @@ -268,7 +285,7 @@ atoms. [Default:] -If not specified, eradius_limit_flag = 0 and pressure_flag = 0. +If not specified, limit_eradius = 0 and pressure_with_evirials = 0. :line