Incorrect args for pair coefficients and TI

Hi all, I have two questions and I am asking both of them in one single post. I am trying to compute solvation free energy of methanol in water using TI. I have come up with this input file for my system

# -- Initialise system --
units real
atom_style full

# -- read data --
read_data system.data

# -- set charges --
set  type  1  charge  -0.8476
set  type  2  charge  0.4238
set  type  3  charge  -0.683
set  type  4  charge  0.418
set  type  5  charge  0.04
set  type  6  charge  0.145

# -- set variables for TI --
variable  lj   equal  0.3
variable  lj1   equal  1
variable  dlj  equal  1
variable  ks   equal  1
variable  ks1   equal  0
variable  dks  equal  1

# -- non bonded interactions --
pair_style lj/cut/coul/long/soft 1  0.5 0.0 10.0 10.0
pair_coeff  1  1  0.1554     3.16557 1.0  
pair_coeff  2  2  0.0        0.0     1.0  
pair_coeff  3  3  0.17       3.12    1.0  
pair_coeff  4  4  0.0        0.0     1.0  
pair_coeff  5  5  0.03       2.5     1.0  
pair_coeff  6  6  0.066      3.5     1.0  
# mixed rules
pair_coeff  1  2  0          0       1.0   
pair_coeff  1  3  0.162536   3.1427  v_lj  
pair_coeff  1  4  0          0       v_lj  
pair_coeff  1  5  0.0682788  2.81317 v_lj  
pair_coeff  1  6  0.101274   3.32859 v_lj  
pair_coeff  2  3  0          0       v_lj  
pair_coeff  2  4  0          0       v_lj  
pair_coeff  2  5  0          0       v_lj  
pair_coeff  2  6  0          0       v_lj  
pair_coeff  3  4  0          0       1.0   
pair_coeff  3  5  0.0714143  2.79285 1.0   
pair_coeff  3  6  0.105925   3.30454 1.0   
pair_coeff  4  5  0          0       1.0   
pair_coeff  4  6  0          0       1.0   
pair_coeff  5  6  0.0444972  2.95804 1.0   


# -- kspace --
kspace_style pppm 0.0001

# -- special bonds --
special_bonds lj/coul 0.0 0.0 0.5

# -- bonded interactions --
bond_style harmonic
bond_coeff 1 553.0 0.945
bond_coeff 2 320.0 1.41
bond_coeff 3 340.0 1.09
bond_coeff 4 600.0 1.0

# -- angular potential --
angle_style harmonic
angle_coeff 1 55.0 108.5
angle_coeff 2 33.0 107.8
angle_coeff 3 35.0 109.5
angle_coeff 4 75.0 109.47

# -- dihedral potential ( only methanol ) --
dihedral_style opls
dihedral_coeff 1 0.0 0.0 0.352 0.0


# -- write ff data --
write_data ff.data pair ij

# -- water shake --
group spc type 1:2
fix myshake spc shake 0.0001 10 100 b 4 a 4

# -- TI --
compute TI all ti lj/cut/coul/long 3*6 v_lj1 v_dlj kspace * v_ks1 v_dks

# -- simulation protocol --
timestep 0.5
minimize 0.0 0.0 1000 10000
velocity all create 300.0 5463576
fix relax1 all npt temp 300.0 300.0 50.0 iso 1.0 1.0 100.0
run 20000
unfix relax1

fix relax2 all npt temp 300.0 300.0 50.0 iso 1.0 1.0 100.0
thermo_style custom step temp press density c_TI
thermo 10
log cg.log
run 20000
write_data prod.data nocoeff

Input structure file:
system.data (88.5 KB)

I read, in a paper to which I am comparing my results to, that soft-core potential was used in their computation. Excerpt from the paper: A linear dependence of the electrostatic interactions with the coupling parameter was imposed. For all four solutes, the soft-core function of Beuler et al. Thus, I made this input script.

I run this script and as one might expect I get an error:

ERROR: Incorrect args for pair coefficients (src/src/FEP/pair_lj_cut_coul_long_soft.cpp:604)
Last command: pair_coeff  2  2  0.0        0.0     1.0

My first question is:
1 ) How to fix this :cry:

The second question pertains to TI.
2) Since the soft core potential already have lambda which scales the interaction, how exactly should I write the compute ti command? I have attempted to write something, does that make sense? If not, how should one go about doing it?

Thank you so much.

Best regards,
Ved

Very bad idea. The forum is archived to allow people in the future to search for responses to similar problems. By conflating two different topics you create a messy and confusing situation.
Thus I’ll only respond to the first part and ask you to post the second part as a separate topic.

Study and follow the documentation!

1 Like

Hi Alex, Thank you so much for your response.

I have made a new post for the second part of the question.

Regarding the documentation, is it possible for your to link where I can look for the solution? I am sorry, but I seem to have missed it in the documentation.

Thank you and regards,
Ved

consider using the search function, or just google or similar.

This is also a good starting point: 5.5. General commands — LAMMPS documentation