Cluster Evolution during the Early Stages of Heating Explosives and its Relationship to Sensitivity: A Comparative Study of TATB, -HMX and PETN by Molecular Reactive Force Field Simulations

Yushi Wen, Chaoyang Zhang,*Xianggui Xue, and Xinping Long

Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), P. O. Box

919-327, Mianyang, Sichuan 621900, China.

Electronic Supplementary Information

Table of Contents

S1. The detailed information of the supercells.

S2. Validation of ReaxFF_lg to this work.

S3. List of bond order minimum values used to determine molecules.

S4. The products in different temperatures of TATB, HMX and PETN.

S5. The evolutions of atom-atom pair correlation functions of TATB, HMX, and PETN heated

at 2500 K.

S6. References

s1

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2015

S1. The detailed information of the supercells

Table s1. The detailed information of the supercellssupercells TATB HMX PETN

enlargement times from unit

cells6×6×6 8×5×5 4×3×7

a b c a b c a b c

54.06 Å

54.17 Å

40.87 Å

52.32 Å

55.25 Å

43.50 Å

53.16 Å

40.47 Å

47.81 Å

α β γ α β γ α β γLattice

Parameters

108.58°119.97

°91.82° 90.00° 90.00° 90.00° 90.00° 90.00° 90.00°

Amounts of molecules

432 400 336

Amounts of atoms

10368 11200 9744

Fig. s1. Supercells of TATB, -HMX and PETN. The carbon, hydrogen, oxygen and nitrogen

atoms are indicated in grey, white, red and blue, respectively.

s2

S2. Validation of ReaxFF_lg to this work

The validity of ReaxFF_lg to the three representatives has also been reexamined in this

work from two aspects: (1) cell geometries and packing densities. 10ps NPT simulations at

273K and atmospheric pressure using ReaxFF_lg were implemented to obtain the initial

configurations of TATB, HMX and PETN; and (2) reaction product kinds. Upon the initial

configurations of three representatives, a 50 ps NVT (3000K) heating simulation was

conducted for each. As results, the NPT simulations showed that the lattice parameters of

TATB, HMX and PETN reduce about -1.6%, -1.2 %, and -1.1% on average, namely, there are

only a 4.76%, 3.5 %, and 3.2% density errors compared with the experimental values,

respectively (Table s2). Table s3 also, indicating that ReaxFF_lg can appropriately describe

the physical processes of TATB, HMX and PETN. The initial chemical species of our thermal

simulations also confirmed that ReaxFF_lg can appropriately describe the chemical behaviors

of TATB, HMX and PETN under high temperatures ().

Table s2. The results of NPT simulations (T=273K and P=1atom)

explosivesLattice parameters

of supercellsExpt. ReaxFF_lg a,b and c error density error

a 54.06 53.19 -1.61%

b 54.17 53.31 -1.59%TATB

c 40.87 40.22 -1.60%

4.76%

a 52.32 51.69 -1.2%

b 55.25 54.59 -1.2%HMX

c 43.50 42.98 -1.2%

3.5%

a 53.16 52.58 -1.1%

b 40.47 39.98436 -1.2%PETN

c 47.81 47.28409 -1.1%

3.2%

s3

Table s3.The initial chemical species of our thermal simulations

TATB HMX PETN

chemical species a DFT CalculationReaxFF_lg

Calculationb Expt. ReaxFF_lg c Expt. ReaxFF_lg

CO2 √ √ √ √ √ √

CO exists √ √ √ √

C(s) exists exists √ exists

H2O √ √ √ √ √ √

N2 √ √ √ √ √ √

H2 exists √ √ √ √ √

CH4 exists √ exists exists exists

HCN exists exists

Other

(very tiny)NCO, NCO2, CN2

NO,NO2,HONO,

HON,NH3,OH,HNot detected

NO,NO2,HONO,

HON,NH3,OH,H,

CON,CH2O

NH3

NO,NO2,HONO,

HON,NH3,OH,

C2O3,CH2O

√-main products

a Calculated by Manaa et al.1

b Observed by Donald L. Ornellas.2

c Observed by Donald L. Ornellas.3

s4

S3. List of bond order minimum values used to determine molecules

Table s4. List of bond order minimum values used to determine molecules.

Atom type Atom type Bond orderC N 0.3C C 0.55C O 0.65C H 0.4O O 0.65N O 0.4O H 0.4H H 0.55H N 0.55N N 0.55

s5

S4. The products in different temperatures of TATB, HMX and PETN

0

50

100

150

200300400500

0

50

100

150

200400600800

1000

0 10 20 30 40 500

50

100

150

200400600800

1000

N fragm

ents

TATB NO2 NO HONO H2O N2 CO2 HON H2 OH NH3 H

(a) 2000 K

(b) 2500 K

N fragm

ents

(c) 3000 K

N fragm

ents

time, ps

Fig. s2. The products in different temperatures of TATB

s6

50

100

150

200300400500600700

50

100

150

250500750

1000

0 10 20 30 40 500

50

100

150

250500750

10001250

HMX NO2 NO HONO H2O CH2O N2 CO2 HON H2 OH NH3 CON H CHON

N fragm

ents

(a) 2000 K

(b) 2500 K

N fragm

ents

(c) 3000 K

N fragm

ents

time, psFig. s3. The products in different temperatures of HMX.

s7

0

50

100

150

200300400500

50

100

150

250500750

1000

0 10 20 30 40 500

50

100

150

250500750

1000

N fragm

ents

PETN NO2 NO HONO H2O CH2O N2 CO2 HON H2 HO NH3 C2O3 O2

(a) 2000 K

(b) 2500 K

N fragm

ents

(c) 3000 K

N fragm

ents

time, ps

Fig. s4. The products in different temperatures of PETN

s8

S5. The evolutions of atom-atom pair correlation functions of TATB, HMX, and PETN heated at 2500 K

5

10

15

20

25

0

1

2

3

4

5

0 2 4 6 8 100

2

4

6

8

10

2 4 6 8 10 2 4 6 8 10

1.45Å C-C 0 ps

1.45Å

C-C 25 ps

1.45Å

C-C 50 ps

2.35Å C-O 0 ps

1.25Å

C-O 25 ps C-O 50 ps

1.25Å

g(r)

g(r)

3.05Å

g(r)

A

N-N 0ps 1.15Å

r

N-N 25 ps 1.15Å

r

N-N 50 ps

Fig. s5．Evolution of atom-atom pair correlation functions of TATB heated at 2500 K.

2468

1012141618

0

1

2

3

4

5

6

7

0 2 4 6 8 100

24

6

8

1012

14

16

2 4 6 8 10 2 4 6 8 10

1.45Å

r r

1.15Å1.15Å

1.35Å

1.25Å1.25Å

2.75Å

1.45Å

2.55Å

N-N 50 psN-N 25 psN-N 0 ps

C-O 50 psC-O 25 psC-O 0 ps

C-C 50 psC-C 25 psC-C 0 ps

g(r)

g(r)

g(r)

r

Fig. s6．Evolution of atom-atom pair correlation functions of HMX heated at 2500 K.

s9

5

10

15

20

25

30

35

2

4

6

8

10

12

0 2 4 6 8 100

5

10

15

20

25

2 4 6 8 10 2 4 6 8 10

1.55Å

g(r)

1.55Å

1.55Å

C-C 25 ps C-C 50 ps

1.45Å

1.15Å

1.15Å

3.75Å

1.25Å1.25Å

N-N 50 psN-N 25 psN-N 0 ps

C-O 50 psC-O 25 psC-O 0 ps

g(r)

g(r)

r r

C-C 0 ps

r

Fig. s7．Evolution of atom-atom pair correlation functions of PETN heated at 2500 K.

We used atom-atom pair correlation functions or radius distribution functions (RDFs, g(r))

shown by Figs. s5-s7 to describe the evolution of heated TATB, HMX and PETN at 2500 K.

For TATB (Fig. s5), the largest g(r) of C-C is always located at r=1.45 Å with different

intensity, suggesting the benzene structures retain during the heating. The largest g(r) of C-O

is transferred from 2.35 to 1.25 Å, denoting the CO and CO2 formation. Similarly, g(r) of N-N

of 1.15 Å suggests the formation of N2. Also, g(r) can used to analyze the reactions in heated

HMX and PETN.

S6. References

(1) M. R. Manaa, E. J. Reed, L. E. Fried, and N. Goldman, J. Am. Chem. Soc. 2009, 131, 5483.

(2) Donald L. Ornellas, The Journal of Physical Chemistry 1968, 72, 2390.

(3) Donald L. Ornellas, John H. Carpenter and Stuart R. Gunn, The Review of Scientific Insturments 1966,

37, 907.s10

s11