Buckingham Potential

Dear LAMMPS users

I’m using this command:

pair_style buck 20

pair_coeff * * 2442.60 0.3054 17.51

cut off= 20A
A= 2442.60 A
rho= 0.3054 eV
C= 17.51 eV A^6

but there is an error saying that these parameters are out of bound. Can anybody help me with this problem. Whats wrong with this command.

Regards
Afza Shahid

Dear LAMMPS users

I'm using this command:

*pair_style buck 20*
*pair_coeff * * 2442.60 0.3054 17.51*

*cut off= 20A*
*A= 2442.60 A*
*rho= 0.3054 eV*
*C= 17.51 eV A^6*

but there is an error saying that these parameters are out of bound. Can
anybody help me with this problem. Whats wrong with this command.

​nothing. ​

Please put the input script lines and the error message in your mail post.

Steve

Dear Steve
I have run the simulation using arbitrary values for coefficients of buckingham potential and there is no error but when I give the actual values of coefficients of Buckingham potential there an error saying All pair coeff are not set. Input script is given below:

---------- Initialize Simulation ---------------------

clear
units metal
dimension 3
boundary p p p
atom_style atomic
atom_modify map array

---------- Create Atoms ---------------------

read_data YzOO.in
#lattice fcc 4
#region box block 0 1 0 1 0 1 units lattice
#create_box 1 box

#lattice fcc 4 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
#create_atoms 1 box
mass 1 88.90
mass 2 91.22
mass 3 16.0
#replicate 1 1 1

---------- Define Interatomic Potential ---------------------

pair_style buck 2.5
pair_coeff 1 3 2442.60 0.3054 17.51 #Y-O interaction
pair_coeff 2 3 1402.57 0.3312 5.10 #Zr-O interaction
pair_coeff 3 3 35686.18 0.2010 32.00 #O-O interaction
neighbor 2.0 bin
neigh_modify every 1 delay 0 check yes

---------- Define Settings ---------------------

compute eng all pe/atom
compute eatoms all reduce sum c_eng

---------- Run Minimization ---------------------

reset_timestep 0
fix 1 all box/relax iso 0.0 vmax 0.001
thermo 10
thermo_style custom step pe lx ly lz press pxx pyy pzz c_eatoms
min_style cg
minimize 1e-25 1e-25 5000 10000

variable natoms equal “count(all)”
variable teng equal “c_eatoms”
variable length equal “lx”
variable ecoh equal “v_teng/v_natoms”

print “Total energy (eV) = {teng};" print "Number of atoms = {natoms};”
print “Lattice constant (Angstoms) = {length};" print "Cohesive energy (eV) = {ecoh};”

print “All done!”

I have run the simulation with the pair coeff command given below (supposed values for coefficients) and it shows no error.
pair_style buck 2.5
pair_coeff * * 100.0 1.5 200.0

Kindly help me where exactly the problem is.

Regards
Afza Shahid.

Please put the input script lines and the error message in your mail post.

Steve

Dear Steve
I have run the simulation using arbitrary values for coefficients of
buckingham potential and there is no error but when I give the actual
values of coefficients of Buckingham potential there an error saying All
pair coeff are not set. Input script is given below:

​that error message is self-explanatory! you are not providing pair_coeff
entries for all pairs of atom types. where are the parameters for Y-Y,
Y-Zr, and Zr-Zr interactions?
if you use pair_coeff * *, you implicitly assign parameters of all pairs of
types.

also, your global non-bonded cutoff of 2.5 angstrom does not make any sense
for a system with metal units. it *must* be wrong.

axel.