Shortcut: FCCUBIC

Module	symfunc
Description	Usage
Measure how similar the environment around atoms is to that found in a FCC structure.
output value	type
the symmetry function for each of the specified atoms	vector

Output components

This action can calculate the values in the following table when the associated keyword is included in the input for the action. These values can be referenced elsewhere in the input by using this Action's label followed by a dot and the name of the value required from the list below.

Name	Type	Keyword	Description
lessthan	scalar	LESS_THAN	the number of colvars that have a value less than a threshold
morethan	scalar	MORE_THAN	the number of colvars that have a value more than a threshold
altmin	scalar	ALT_MIN	the minimum value of the cv
min	scalar	MIN	the minimum colvar
max	scalar	MAX	the maximum colvar
between	scalar	BETWEEN	the number of colvars that have a value that lies in a particular interval
highest	scalar	HIGHEST	the largest of the colvars
lowest	scalar	LOWEST	the smallest of the colvars
sum	scalar	SUM	the sum of the colvars
mean	scalar	MEAN	the mean of the colvars

Input

The atoms that serve as the input for this action are specified using one or more of the keywords in the following table.

Keyword	Type	Description
SPECIES	atoms	the list of atoms for which the symmetry function is being calculated and the atoms that can be in the environments
SPECIESA	atoms	the list of atoms for which the symmetry function is being calculated
SPECIESB	atoms	the list of atoms that can be in the environments of each of the atoms for which the symmetry function is being calculated

Further details and examples

Measure how similar the environment around atoms is to that found in a FCC structure.

This shortcut is an example of a COORDINATION_SHELL_AVERAGE, which we can use to measure how similar the environment around atom $i$ is to an fcc structure. The function that is used to make this determination is as follows:

$s_i = \frac{ \sum_{i \ne j} \sigma(r_{ij}) \left\{ a\left[ \frac{(x_{ij}y_{ij})^4 + (x_{ij}z_{ij})^4 + (y_{ij}z_{ij})^4}{r_{ij}^8} - \frac{\alpha (x_{ij}y_{ij}z_{ij})^4}{r_{ij}^{12}} \right] + b \right\} }{ \sum_{i \ne j} \sigma(r_{ij}) }$

In this expression $x_{ij}$ , $y_{ij}$ and $z_{ij}$ are the $x$ , $y$ and $z$ components of the vector connecting atom $i$ to atom $j$ and $r_{ij}$ is the magnitude of this vector. $\sigma(r_{ij})$ is a switching function that acts on the distance between atom $i$ and atom $j$ and its inclusion in the numerator and the denominator of the above expression as well as the fact that we are summing over all of the other atoms in the system ensures that we are calculating an average of the function of $x_{ij}$ , $y_{ij}$ and $z_{ij}$ for the atoms in the first coordination sphere around atom $i$ . Lastly, $\alpha$ is a parameter that can be set by the user, which by default is equal to three. The values of $a$ and $b$ are calculated from $\alpha$ using:

$a = \frac{ 80080}{ 2717 + 16 \alpha} \qquad \textrm{and} \qquad b = \frac{ 16(\alpha - 143) }{2717 + 16\alpha}$

This action was been used in all the articles in the bibliography. We thus wrote an explict action to calculate it in PLUMED instead of using a shortcut as we did for SIMPLECUBIC so that we could get good computational performance.

The following input calculates the FCCUBIC parameter for the 64 atoms in the system and then calculates and prints the average value for this quantity.

Click on the labels of the actions for more information on what each action computes

dThe FCCUBIC action with label d calculates the following quantities: Quantity    Type    Description  
d vector the symmetry function for each of the specified atoms
d_mean scalar the mean of the colvars: FCCUBICMeasure how similar the environment around atoms is to that found in a FCC structure. This action is a shortcut and it has hidden defaults. More details SPECIESthe list of atoms for which the symmetry function is being calculated and the atoms that can be in the environments=1-64 SWITCHthe switching function that it used in the construction of the contact matrix. Options for this keyword are explained in the documentation for LESS_THAN.={RATIONAL D_0=3.0 R_0=1.5} MEAN calculate the mean of all the quantities
d: FCCUBICMeasure how similar the environment around atoms is to that found in a FCC structure. This action is a shortcut and uses the defaults shown here. More details SPECIESthe list of atoms for which the symmetry function is being calculated and the atoms that can be in the environments=1-64 SWITCHthe switching function that it used in the construction of the contact matrix. Options for this keyword are explained in the documentation for LESS_THAN.={RATIONAL D_0=3.0 R_0=1.5} MEAN calculate the mean of all the quantities  PHI The Euler rotational angle phi=0.0 THETA The Euler rotational angle theta=0.0 PSI The Euler rotational angle psi=0.0 ALPHA The alpha parameter of the angular function that is used for FCCUBIC=3.0
# PLUMED interprets the command:
# d: FCCUBIC SPECIES=1-64 SWITCH={RATIONAL D_0=3.0 R_0=1.5} MEAN
# as follows (Click the red comment above to revert to the short version of the input):
d_grpThe GROUP action with label d_grp calculates the following quantities: Quantity    Type    Description  
d_grp atoms indices of atoms specified in GROUP: GROUPDefine a group of atoms so that a particular list of atoms can be referenced with a single label in definitions of CVs or virtual atoms. More details ATOMSthe numerical indexes for the set of atoms in the group=1-64
d_matThe CONTACT_MATRIX action with label d_mat calculates the following quantities: Quantity    Type    Description  
d_mat.w matrix a matrix containing the weights for the bonds between each pair of atoms
d_mat.x matrix the projection of the bond on the x axis
d_mat.y matrix the projection of the bond on the y axis
d_mat.z matrix the projection of the bond on the z axis: CONTACT_MATRIXAdjacency matrix in which two atoms are adjacent if they are within a certain cutoff. More details GROUPspecifies the list of atoms that should be assumed indistinguishable=1-64 SWITCHthe input for the switching function that acts upon the distance between each pair of atoms. Options for this keyword are explained in the documentation for LESS_THAN.={RATIONAL D_0=3.0 R_0=1.5} COMPONENTS also calculate the components of the vectors connecting the atoms in the contact matrix
d_vfuncThe FCCUBIC_FUNC action with label d_vfunc calculates the following quantities: Quantity    Type    Description  
d_vfunc matrix the matrix obtained by doing an element-wise application of a function that measures the similarity with an fcc environment to the input matrix: FCCUBIC_FUNCMeasure how similar the environment around atoms is to that found in a FCC structure. More details ARGthe values input to this function=d_mat.x,d_mat.y,d_mat.z ALPHA The alpha parameter of the angular function=3.0
d_wvfuncThe CUSTOM action with label d_wvfunc calculates the following quantities: Quantity    Type    Description  
d_wvfunc matrix the matrix obtained by doing an element-wise application of an arbitrary function to the input matrix: CUSTOMCalculate a combination of variables using a custom expression. More details ARGthe values input to this function=d_vfunc,d_mat.w FUNCthe function you wish to evaluate=x*y PERIODICif the output of your function is periodic then you should specify the periodicity of the function=NO
d_onesThe CONSTANT action with label d_ones calculates the following quantities: Quantity    Type    Description  
d_ones vector the constant value that was read from the plumed input: ONESCreate a constant vector with all elements equal to one More details SIZEthe number of ones that you would like to create=64
dThe MATRIX_VECTOR_PRODUCT action with label d calculates the following quantities: Quantity    Type    Description  
d vector the vector that is obtained by taking the product between the matrix and the vector that were input: MATRIX_VECTOR_PRODUCTCalculate the product of the matrix and the vector More details ARGthe label for the matrix and the vector/scalar that are being multiplied=d_wvfunc,d_ones
d_denomThe MATRIX_VECTOR_PRODUCT action with label d_denom calculates the following quantities: Quantity    Type    Description  
d_denom vector the vector that is obtained by taking the product between the matrix and the vector that were input: MATRIX_VECTOR_PRODUCTCalculate the product of the matrix and the vector More details ARGthe label for the matrix and the vector/scalar that are being multiplied=d_mat.w,d_ones
d_nThe CUSTOM action with label d_n calculates the following quantities: Quantity    Type    Description  
d_n vector the vector obtained by doing an element-wise application of an arbitrary function to the input vectors: CUSTOMCalculate a combination of variables using a custom expression. More details ARGthe values input to this function=d,d_denom FUNCthe function you wish to evaluate=x/y PERIODICif the output of your function is periodic then you should specify the periodicity of the function=NO
d_meanThe MEAN action with label d_mean calculates the following quantities: Quantity    Type    Description  
d_mean scalar the mean of all the elements in the input vector: MEANCalculate the arithmetic mean of the elements in a vector More details ARGthe values input to this function=d_n PERIODICif the output of your function is periodic then you should specify the periodicity of the function=NO
# --- End of included input --- PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=d.* FILEthe name of the file on which to output these quantities=colv

Notice that you can you can rotate the bond vectors before computing the function in the above expression as is discussed in the documentation for COORDINATION_SHELL_FUNCTION

References

More information about how this action can be used is available in the following articles: - A. D. White, G. A. Voth, Efficient and Minimal Method to Bias Molecular Simulations with Experimental Data. Journal of Chemical Theory and Computation. 10, 3023–3030 (2014) - S. Angioletti-Uberti, M. Ceriotti, P. D. Lee, M. W. Finnis, Solid-liquid interface free energy through metadynamics simulations. Physical Review B. 81 (2010) - B. Cheng, G. A. Tribello, M. Ceriotti, Solid-liquid interfacial free energy out of equilibrium. Physical Review B. 92 (2015) - B. Cheng, G. A. Tribello, M. Ceriotti, The Gibbs free energy of homogeneous nucleation: From atomistic nuclei to the planar limit. The Journal of Chemical Physics. 147 (2017) - B. Cheng, M. Ceriotti, G. A. Tribello, Classical nucleation theory predicts the shape of the nucleus in homogeneous solidification. The Journal of Chemical Physics. 152 (2020)

Syntax

The following table describes the keywords and options that can be used with this action

Keyword	Type	Default	Description
SPECIES	input	none	the list of atoms for which the symmetry function is being calculated and the atoms that can be in the environments
SPECIESA	input	none	the list of atoms for which the symmetry function is being calculated
SPECIESB	input	none	the list of atoms that can be in the environments of each of the atoms for which the symmetry function is being calculated
NN	compulsory	6	The n parameter of the switching function
MM	compulsory	0	The m parameter of the switching function; 0 implies 2*NN
D_0	compulsory	0.0	The d_0 parameter of the switching function
R_0	compulsory	none	The r_0 parameter of the switching function
FUNCTION	compulsory	none	the function of the bond vectors that you would like to evaluate
PHI	compulsory	0.0	The Euler rotational angle phi
THETA	compulsory	0.0	The Euler rotational angle theta
PSI	compulsory	0.0	The Euler rotational angle psi
ALPHA	compulsory	3.0	The alpha parameter of the angular function that is used for FCCUBIC
SWITCH	optional	not used	the switching function that it used in the construction of the contact matrix. Options for this keyword are explained in the documentation for LESS_THAN.
LESS_THAN	optional	not used	calculate the number of variables that are less than a certain target value. Options for this keyword are explained in the documentation for LESS_THAN.
MORE_THAN	optional	not used	calculate the number of variables that are more than a certain target value. Options for this keyword are explained in the documentation for MORE_THAN.
ALT_MIN	optional	not used	calculate the minimum value
MIN	optional	not used	calculate the minimum value
MAX	optional	not used	calculate the maximum value
BETWEEN	optional	not used	calculate the number of values that are within a certain range. Options for this keyword are explained in the documentation for BETWEEN.
HIGHEST	optional	false	this flag allows you to recover the highest of these variables
HISTOGRAM	optional	not used	calculate a discretized histogram of the distribution of values
LOWEST	optional	false	this flag allows you to recover the lowest of these variables
SUM	optional	false	calculate the sum of all the quantities
MEAN	optional	false	calculate the mean of all the quantities
LOWMEM	optional	false	this flag does nothing and is present only to ensure back-compatibility

Keys	Action
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Quantity	Type	Description
d	vector	the symmetry function for each of the specified atoms
d_mean	scalar	the mean of the colvars