Supporting Information

The Co-crystal of TNT/CL-20 leads to Decreased Sensitivity toward

Thermal Decomposition from First Principles Based Reactive

Molecular Dynamics Dezhou Guo, a,b Qi An, b Sergey V. Zybin, b William A. Goddard III FRSC b,*, Fenglei Huang, a

and Bin Tang b

a State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, People’s Republic of China.b Materials and Process Simulation Center, 139-74, California Institute of Technology, Pasadena, California 91125, USA.* Corresponding author: email: wag@wag.caltech.edu.

Table S1. Bond order cut-off values for different atom pairs. BondFrag program uses these values as a default parameter set (can be adjusted by the user) to determine molecular fragments.

C H O N

C 0.55 0.40 0.80 0.30

H 0.55 0.40 0.55

O 0.65 0.55

N 0.45

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2015

0 20 40 60 80 100-0.8

-0.6

-0.4

-0.2

0.0

0.2

CL-20cocrystal

TNT

1200K

Pote

ntia

l ene

rgy/

mas

s (K

cal/g

)

Time (ps)

0 2 4 6 8 10-0.02

0.00

0.02

0 20 40 60 80 100-0.8

-0.6

-0.4

-0.2

0.0

0.2

CL-20

cocrystal

TNT

1500K

Pote

ntia

l ene

rgy/

mas

s (K

cal/g

)

Time (ps)

0 1 2 3 4 5 6-0.06-0.04-0.020.000.02

A

0 20 40 60 80 100-0.8

-0.6

-0.4

-0.2

0.0

0.2

CL-20

cocrystal

TNT

1750K

Poten

tial e

nerg

y/m

ass (

Kcal/

g)

Time (ps)

0 1 2 3

-0.02

0.00

0.02

0 20 40 60 80 100-0.8

-0.6

-0.4

-0.2

0.0

0.2

CL-20

cocrystal

TNT

2000K

Poten

tial e

nerg

y/m

ass (

Kcal/

g)

Time (ps)

0 1 2 3

-0.02

0.00

0.02

Figure S1. Evolution of potential energy in the NVT MD simulations of CL-20, cocrystal and TNT. The initial potential energy is set to zero as a reference. For CL-20 and the cocrystal, the rate of potential energy decrease depends strongly on the temperature; whereas TNT does not react significantly under the conditions studied here. At each temperature, the energy release rate of CL-20 is faster than that of cocrystal, which is much faster than TNT.

0 20 40 60 80 1000

2

4

6

8

HO H2ON2ONO HONOCL-20 N2

NO2TNT

cocrystal1200K

fragm

ents/

volu

me (

nm-3)

Time (ps)0 20 40 60 80 100

0

2

4

6

8

HONON2ONO HO H2O

N2

CL-20 NO2

Time (ps)

fragm

ents/

volu

me (

nm-3) CL-201200K

0 20 40 60 80 1000

2

4

6

8

CO2

N2

H2OHON2O

HONONO

CL-20

TNT

NO2

Time (ps)

fragm

ents/

volu

me (

nm-3) cocrystal1500K

0 20 40 60 80 1000

2

4

6

8

H2OCO2N2OHONO

HONOCL-20

NO2

N2

Time (ps)

fragm

ents/

volu

me (

nm-3) CL-201500K

0 20 40 60 80 1000

2

4

6

8

N2

H2OCO2

HON2OHONONOCL-20

TNT

NO2

cocrystal1750K

fragm

ents/

volu

me (

nm-3)

Time (ps)

0 20 40 60 80 1000

2

4

6

8

HOfragm

ents/

volu

me (

nm-3)

Time (ps)

CO2NON2OHONO

CL-20H2O

N2

NO2

CL-201750K

0 20 40 60 80 1000

2

4

6

8

N2OCO2HONOHONO

H2O

CL-20

N2NO2

TNT

cocrystal2000K

fragm

ents/

volu

me (

nm-3)

Time (ps)

0 20 40 60 80 1000

2

4

6

8

N2

H2O

CO2N2OHONOHONO

CL-20

NO2CL-20

2000K

fragm

ents/

volu

me (

nm-3)

Time (ps)

Figure S2. Evolution of intermediate and secondary products of cocrystal and CL-20 of NVT MD. chemical reactions occur more intensely in CL-20 than in cocrystal at each temperature. NO2 is the dominant products in the early stage of CL-20 dissociation.

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cocrystal1200K

No.

of c

arbo

n cl

uste

r (nm

-3)

C8-C12 C13-C17 >=C18

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CL-201200K

No.

of c

arbo

n cl

uste

r (nm

-3)

C8-C12 C13-C17 >=C18

Time (ps)

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cocrystal

No.

of c

arbo

n cl

uste

r (nm

-3)

1500K

C8-C12 C13-C17 >=C18

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7CL-201500K

No.

of c

arbo

n cl

uste

r (nm

-3)

Time (ps)

C8-C12 C13-C17 >=C18

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cocrystal1750K

No.

of c

arbo

n cl

uste

r (nm

-3)

C8-C12 C13-C17 >=C18

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CL-201750K

No.

of c

arbo

n cl

uste

r (nm

-3)

Time (ps)

C8-C12 C13-C17 >=C18

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

No

. of c

arbo

n clu

ster (

nm-3) cocrystal2000K

C8-C12 C13-C17 >=C18

Time (ps)0 20 40 60 80 100

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

No

. of c

arbo

n clu

ster (

nm-3)

Time (ps)

CL-202000K

C8-C12 C13-C17 >=C18

Figure S3. Time evolution of three types of carbon clusters formed for cocrystal and CL-20 during NVT-MD simulation. More and larger carbon-rich aggregates are observed in cocrystal than CL-20, leading to a slower chemical reaction process.

0 10 20 30 40 50 60-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

CL-20

cocrystal

1200K

Pote

ntia

l ene

rgy/

mas

s (K

cal/g

)

Time (ps)0 10 20 30 40 50 60

0

1000

2000

3000

4000

5000

6000

CL-20

cocrystal

1200K

Tem

pera

ture

(K)

Time (ps)

0 10 20 30 40 50 60-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

CL-20

TNT

cocrystal

1500 K

Pote

ntia

l ene

rgy/

mas

s (K

cal/g

)

Time (ps)0 10 20 30 40 50 60

0

1000

2000

3000

4000

5000

6000

TNT

cocrystalCL-20

1500 K

Tem

pera

ture

(K)

Time (ps)

0 10 20 30 40 50 60-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

CL-20cocrystal

TNT

1750K

Pote

ntia

l ene

rgy/

mas

s (K

cal/g

)

Time (ps)0 10 20 30 40 50 60

0

1000

2000

3000

4000

5000

6000

TNT

cocrystal

CL-20

1750K

Tem

pera

ture

(K)

Time (ps)

0 10 20 30 40 50 60-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

CL-20

cocrystal

TNT 2000 K

Poten

tial e

nerg

y/m

ass (

Kcal/

g)

Time (ps)0 10 20 30 40 50 60

0

1000

2000

3000

4000

5000

6000

TNT

cocrystal

CL-20

2000 K

Tem

pera

ture

(K)

Time (ps)

Figure S4. Normalized potential energy and temperature as a function of time during the NVE-MD with initial temperatures T = 1200, 1500, 1750 and 2000 K. The initial potential energy is set to zero as a reference.

0 10 20 30 40 50 600

2

4

6

8

10

12

14

1200 K cocrystal

NO H2O HO HONON2O

NO2CL-20 TNT

No.

of f

ragm

ents/

volu

me (

nm-3)

Time (ps)0 10 20 30 40 50 60

0

2

4

6

8

10

12

14

CO2HONO H2OHONO N2O

CL-20 NO2

N2

CL-201200 K

No.

of f

ragm

ents/

volu

me (

nm-3)

Time (ps)

0 10 20 30 40 50 600

2

4

6

8

10

12

14

CO2

N2

HONOHOH2O

NON2O

CL-20TNT

NO2

cocrystal1500 K

No.

of f

ragm

ents/

volu

me (

nm-3)

Time (ps)0 10 20 30 40 50 60

0

2

4

6

8

10

12

14

N2

CO2

H2O

HON2O NO HONO

NO2

CL-20

1500 KCL-20

No.

of f

ragm

ents/

volu

me (

nm-3)

Time (ps)

0 10 20 30 40 50 600

2

4

6

8

10

12

14

cocrystal

HONO

N2O

NO

HOCO2

TNT

H2O

N2

CL-20

NO2

1750K

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

Time (ps)0 10 20 30 40 50 60

0

2

4

6

8

10

12

14CL-20

CL-20 NON2O

HONO HO

H2O

CO2

N2

NO2

1750K

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

Time (ps)

0 10 20 30 40 50 600

2

4

6

8

10

12

14

H2O CO2

HONO HONON2OCL-20

TNT

N2

NO2

cocrystal2000 K

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

Time (ps)0 10 20 30 40 50 60

0

2

4

6

8

10

12

14

2000 K CL-20

CL-20

N2O

H2O

HO

CO2

NOHONO

NO2

N2

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

Time (ps)

Figure S5. Time evolution of chemical products during the NVE-MD after heating to1200, 1500, 1750 and 2000 K.

0 10 20 30 40 50 600.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cocrystal1200 K

C8-C12 C13-C17 >=C18

No.

of c

arbo

n cl

uste

r/vol

ume (

nm-3)

Time (ps)0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CL-201200 K

C8-C12 C13-C17 >=C18

No.

of c

arbo

n cl

uste

r/vol

ume (

nm-3)

Time (ps)

0 10 20 30 40 50 600.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cocrystal1500 K

C8-C12 C13-C17 >=C18

No.

of c

arbo

n cl

uste

r/vol

ume (

nm-3)

Time (ps)0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CL-201500 K

C8-C12 C13-C17 >=C18

No.

of c

arbo

n cl

uste

r/vol

ume(

nm-3)

Time (ps)

0 10 20 30 40 50 600.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cocrystal

1750K

C8-C12 C13-C17 >=C18

No.

of c

arbo

n cl

uste

r/vol

ume (

nm-3)

Time (ps)0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1750K CL-20

C8-C12 C13-C17 >=C18

No. o

f car

bon c

luste

r/vol

ume(

nm-3)

Time (ps)

0 10 20 30 40 50 600.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

2000 Kcocrystal

C8-C12 C13-C17 >=C18

No.

of c

arbo

n cl

uste

r/vol

ume(

nm-3)

Time (ps)0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CL-202000 K

C8-C12 C13-C17 >=C18

No. o

f car

bon

cluste

r/vol

ume(

nm-3)

Time (ps)

Figure S6. Time evolution of three types of carbon cluster formed during NVE-MD for cocrystal and CL-20.

0 20 40 60 80 1000

1

2

3

4

5

mixture

TNT

N2

H2O HOHONO NO

N2OCL-20

NO2

Time (ps)

No.

of f

ragm

ents/

volu

me (

nm-3)

1200K

0 20 40 60 80 1000

1

2

3

4

5

HO H2ON2ONO

HONOCL-20 N2

NO2TNT

cocrystal1200K

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

Time (ps)

0 20 40 60 80 1000

1

2

3

4

5

mixture

NOCO2HO

N2

H2OHONO

N2OCL-20

TNT

NO2

Time (ps)

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

1500K

0 20 40 60 80 1000

1

2

3

4

5

CO2

N2

H2O

HON2O

HONONO

CL-20

TNT

NO2

Time (ps)

No.

of f

ragm

ents/

volu

me (

nm-3)

cocrystal1500K

0 20 40 60 80 1000

1

2

3

4

5

mixture

CO2HONO

H2O

HO

N2

N2O

NOCL-20

TNT

NO2

Time (ps)

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

2000K

0 20 40 60 80 1000

1

2

3

4

5

HONO N2O CO2

HO

NONO

H2O

CL-20

N2

NO2

TNT

cocrystal2000K

No. o

f fra

gmen

ts/vo

lum

e (nm

-3)

Time (ps)

Figure S7. Evolution of intermediate and secondary products of mixture and cocrystal during NVT-MD simulations.