pair style table

Dear lammps-users

I have a problem using tabulated potentials. In detail I want to simulate a nanoparticle in water. For that purpose I have 3 different types of tabulated potentials Water-water, water-particle and particle-particle.

When I just run a pure water simulation (using water-water potential only ) then everything is fine. But as soon as I add the nanoparticles (and with that the water-particle and particle-particle potential) I receive the error message:

Pair distance < table inner cutoff (pair_table.cpp:119)

The three types of potentials have of course very different values of inner and outer cutoffs as you can see below.

when one plots the potentials they are perfectly smooth and F = -grad U is satisfied.

Potential for Silica-Water

SiO-H2O

N 200 R 13.85 30.05

1 13.85000 1667286. 4333738.

2 14.05000 995072.2 2549651.

3 14.25000 598227.4 1511311.

4 14.45000 362208.6 902388.2

5 14.65000 220824.4 542640.3

6 14.85000 135534.3 328568.2

7 15.05000 83731.23 200287.4

8 15.25000 52057.89 122890.8

9 15.45000 32566.89 75884.01

10 15.65000 20496.76 47149.09

11 15.85000 12976.23 29472.82

12 16.05000 8262.307 18532.28

13 16.25000 5290.302 11720.05

14 16.45000 3405.876 7453.588

15 16.65000 2204.390 4766.249

16 16.85000 1434.183 3064.130

17 17.05000 937.8301 1980.169

18 17.25000 616.3010 1286.193

19 17.45000 406.9742 839.6030

20 17.65000 270.0175 550.7441

21 17.85000 179.9801 362.9850

22 18.05000 120.5098 240.3520

Potential for Water

H2O

N 200 R 2.0 5.98

1 2.0000000 347.72549 1185.8064

2 2.0200000 324.55002 1145.2435

3 2.0400000 301.91577 1104.6807

4 2.0599999 280.36279 1064.1179

5 2.0799999 259.35101 1023.5551

6 2.0999999 239.42058 982.99225

7 2.1199999 220.03131 942.42938

8 2.1400001 201.72340 901.86664

9 2.1600001 183.95674 861.30377

10 2.1799998 167.27132 820.74097

11 2.2000000 151.12715 780.17810

12 2.2200000 136.06418 739.61523

13 2.2400000 121.54252 699.05249

14 2.2600000 108.10208 658.48969

15 2.2800000 95.202934 617.92682

16 2.3000000 83.385010 577.36401

17 2.3199999 72.108299 536.80115

18 2.3399999 61.912964 496.23834

19 2.3600001 52.258762 455.67551

20 2.3800001 43.685955 415.11270

21 2.3999999 35.654270 374.54984

22 2.4200001 28.703959 333.98700

Potential for SiO

SiO

N 200 R 30.2 55.0

1 30.20000 1486143. 1771561.

2 30.40000 1171822. 1387684.

3 30.60000 925422.8 1088733.

4 30.80000 731955.9 855533.0

5 31.00000 579814.9 673333.4

6 31.20000 459985.9 530752.9

7 31.40000 365463.2 419002.4

8 31.60000 290787.6 331277.0

9 31.80000 231704.3 262306.8

10 32.00000 184889.3 208000.5

11 32.20000 147740.4 165175.6

12 32.40000 118219.8 131355.3

13 32.60000 94727.85 104607.4

14 32.80000 76006.85 83422.14

15 33.00000 61067.45 66619.05

16 33.20000 49129.14 53272.56

17 33.40000 39576.53 42657.34

18 33.60000 31922.59 34202.78

19 33.80000 25781.62 27459.72

20 34.00000 20848.29 22074.66

21 34.20000 16879.90 17768.32

22 34.40000 13683.79 14320.25

23 34.60000 11106.37 11555.76

24 34.80000 9025.220 9336.435

25 35.00000 7342.804 7552.598

26 35.20000 5981.011 6116.943

27 35.40000 4877.455 4960.124

28 35.60000 3982.098 4026.841

29 35.80000 3254.792 3272.975

30 36.00000 2663.308 2663.308

31 36.20000 2181.737 2169.683

In my in file I use

pair_style table linear 200

pair_coeff 1 1 water.table H2O 5.8

pair_coeff 1 2 water.SiO.table SiO-H2O 29.85

pair_coeff 2 2 SiO.table SiO 55.0

Now my questions:

  1. should all the potentials be in the same resolution when I just use linear interpolation (here water-water 0.02 and the others 0.2) ?

  2. should all potentials have the same number of data points?

  3. How can the distance between the atoms become smaller than the inner cutoff if the forces are so strongly repulsive there?

Are their and suggestions of what I am doing wrong in my simulations?

Thank you very much

Sabine

  1. should all the potentials be in the same resolution when I just use linear interpolation (here water-water 0.02 and the others 0.2) ?

  2. should all potentials have the same number of data points?

  3. How can the distance between the atoms become smaller than the inner cutoff if the forces are so strongly repulsive there?

The answer to (1,2) is up to you. It’s your tabulated model.
The answer to 3 is probably bad dynamics, or the interpolated
tables may not be as smooth as you think (you can make
a plot of each of the 3, as LAMMPS views it, using the pair_write
command).

I suggest you add a print statement in the code where the error
message is appearing and verify that a pair of particles are closer
than the inner cutoff of the corresponding table. If they are,
then you need to fix your dynamics.

Steve