army research office military university research initiative oct 16, 2003

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ARMY RESEARCH OFFICE Military University Research Initiative Oct 16, 2003 Quantum Theory Project Departments of Chemistry and Physics University of Florida Gainesville, Florida USA Rodney J. Bartlett Co-Workers Mr. Andrew Taube Mr. Josh McClellan Mr. Tom Hughes Mr.Luis Galiano Dr. Stefan Fau Dr. DeCarlos Taylor (ARL) Dr. Ariana Beste (ORNL)

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ARMY RESEARCH OFFICE Military University Research Initiative Oct 16, 2003. Rodney J. Bartlett. Co-Workers Mr. Andrew Taube Mr. Josh McClellan Mr. Tom Hughes Mr.Luis Galiano Dr. Stefan Fau. Dr. DeCarlos Taylor (ARL) Dr. Ariana Beste (ORNL). Quantum Theory Project - PowerPoint PPT Presentation

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Page 1: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

ARMY RESEARCH OFFICE

Military University Research Initiative Oct 16, 2003

Quantum Theory ProjectDepartments of Chemistry and Physics

University of FloridaGainesville, Florida USA

Rodney J. Bartlett Co-Workers

Mr. Andrew Taube Mr. Josh McClellanMr. Tom Hughes Mr.Luis Galiano

Dr. Stefan FauDr. DeCarlos Taylor (ARL)Dr. Ariana Beste (ORNL)

Page 2: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Identify and characterize the initial steps in nitramine and other detonation in the condensed phase.

Progress requries NEW ab initio quantum mechancial techniques that have the accuracy and appicability to provide reliable results for unimolecular and bimolecular reaction paths.

Study the series of molecules, nitramine (gas phase), methyl nitramine(liquid), dimethylnitramine(solid) which have (1) different reaction paths(2) different condensed phase effects

Investigate their unimolecular, secondary, and bimolecular reaction mechanisms.

Obtain definitive results for the comparative activation barriers for different unimolecular paths, particularly for RDX.

Study the nitromethane molecule and its various isomers as a prototype for nitroalkanes.

Generate ‘transfer Hamiltonians’ to enable direct dynamics simulations as a QM compliment to classical potentials, and to be able to reliably describe many units of a condensed phase explosive.

Provide high-level QM results to facilitate the development of classical PES for large scale simulations.

University of Florida: Quantum Theory Project

OBJECTIVES

Page 3: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Quantum Mechanics I (Isolated gas phase molecules, 0K)Potential Energy Surface E(R) Different Unimolecular Decomposition PathsActivation BarriersSpectroscopic signatures for intermediates and products

Quantum Mechanics IIBi(tri...)molecular reactionsLong range (condensed phase, pressure) effectsActivation Barriers, Spectroscopy

Classical Mechanics-- Representation E(R)

Large Molecule QM--Simplified Representationof H(R) Transfer HamiltonianElectronic State Specific

Page 4: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Reactions of one Me2N-NO2

Me2N-NO2 Me2N. + NO2

.

MeN.-NO2 + Me.

H2C.-N(Me)-NO2 + H.

[ H2C=N+(Me)-N(O-)OH] H2C=NMe + HONO

Page 5: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Reactions of two Me2N-NO2

Same reactions as before, causing a slight change in the interaction

energy with the second Me2N-NO2.

Additionally:

Me2N-NO2 + Me2N-NO2 Me2N-ONO + Me2N. + NO2

.

Me2N-NMe2 + NO2. + NO2

.

Me2N-Me + Me-N.-NO2 + NO2.

Me2N-N(Me)-NO2 + Me. + NO2.

Me2N-H + H2C.-N(Me)-NO2 + NO2

.

Me2N-CH2-N(Me)-NO2 + H. + NO2.

products from CH3., H. (HONO, H-Me, …)

Page 6: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

In reposne to Bob Shaw’s comment abouterror bars in theoretical applications….

It is clear that if we want to know the right answerfor activation barriers competitive decompisiton paths..

We need a high-level of theory like CCSD(T), with a large basis set.

Page 7: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Coupled Cluster Calculation of De’s

De (kcal/mol)

0.0

0.2

0.4

0.6

0.8

1.0

-40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0

MP2

CCSD(T)

CCSD

MP2 CCSD +(T)

6.0 -8.3 -1.0

std 7.5 4.5 0.5

(De)

From K. L. Bak et al., J. Chem. Phys. 112, 9229-9242 (2000)

Page 8: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Last year…

•Reported the detailed theory for the compressed (SVD) CC, which ‘contracts’ the CC amplitudes in an optimum way to make it possible to perform much higher level CC calculations for large molecules.

Page 9: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Potenrial Energy Curve (1) (HF, aug-cc-pVDZ, HF-bond stretcing)

-300

-250

-200

-150

-100

-50

0

0.5 1 1.5 2 2.5 3 3.5 4

MRCI

CCSD

CCSD(T)

CCSDT-1

COMP.SDT-1

(E+

10

0)*

10

00

(a

.u.)

r(HF)/r(eq)

r(eq)=1.733 bohr=0.25

Page 10: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Potential Energy Curve (2) (H2O, aug-cc-pVDZ, OH-bonds

stretching)

-300

-200

-100

0

100

0.5 1 1.5 2 2.5 3 3.5

MRCI

CCSD

CCSD(T)

COMP.SDT-1

CCSDT-1

(E+

76

)*1

00

0 (

a.u

.)

r(OH)/r(eq)

r(eq)=1.809 bohr=0.25

Page 11: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

•Detailed a new extrapolation procedure for energies and forces that has a mean error of nearly zero, and a maximum error of0.75 kcal/mol for nitramne and its components.

•Reported on a series of CC studies of nitramine to assess its decomposition paths.

This year….

Page 12: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

I.A NEW APPROACHE TO HIGH-LEVEL COUPLED-CLUSTER THEORY FOR LARGER MOLECULES.

A. A natural orbital coupled-cluster method.

B. Comparisons to Compressed coupled-cluster theory.

II. NUMERICAL ILLUSTRATIONS FOR DMNA, DMNA DIMERS AND RDX.

Iii. CONCEPT OF A TRANSFER HAMILTONIAN AS A MEANS TO DESCRIBE COMPLEX SYSTEMS WITH QUANTUM MECHANCIAL FORCES FOR MD APPLICATIONS.

A. Illustration for nitromethane and its isomers.

University of Florida: Quantum Theory Project

OUTLINEOUTLINE

Page 13: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

How can we retain the accuracy of CCSD(T), ie an ~n7

method, but make it applicable to large molecules?

Dimer (bimolecular sytem) is 28 times as difficult as the monomer, without modification.

I. Natural orbital coupled-cluster theory

II. Compressed coupled-cluster using Singular Value Decomposition.

Page 14: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Frozen Natural Orbital Coupled Cluster Theory

• Dependence on size of virtual sector of basis set limits high-level CC to small molecules:

• CCSD ~ V4; CCSD(T) ~ V4; CCSDT ~ V5

• Natural Orbitals (NOs) are known to be the best possible set of orbitals to truncate

• Too costly to get exact – use approximate MBPT(2) NOs

• To maintain advantages of a HF reference, only perform truncation in virtual space – leaving occupied space alone – Frozen Natural Orbitals (FNOs)

Page 15: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

FNO Procedure SCF gives Molecular Orbitals U Construct MBPT(2) Density Matrix D in MO

Basis Solve DV=Vn Truncate V to V’ throwing out less occupied

virtuals, as measured by their occupation numbers.

Construct new Fock Matrix in FNO Virtual Space Diagonalize for new orbital energies Perform higher level (CC) calculation in

truncated virtual space For an estimate of truncation error, define:∆MBPT(2) = MBPT(2) (Full) – MBPT(2)

(Truncated)

Page 16: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Note: On the following slides, the percentage listed indicated the number of FNOs retained. For example, 20% DZP means that there are only 20% of the original number of DZP virtual orbitals left.

Computational Details: Calculations were performed on an IBM RS/6000 375 MHz POWER3 processor with 3 GB RAM and 18 GB disk using the ACES II electronic structureprogram.

Page 17: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Three Different Bases. Same Number of Orbitals.

-100.45

-100.4

-100.35

-100.3

-100.25

-100.2

-100.15

-100.1

-100.05

0.5 1 1.5 2 2.5 3

Bond Length (Angstroms)

To

tal E

ner

gy

(Har

tree

)

100% DZP

40% cc-pVTZ

20% cc-pVQZ

100% cc-pVQZ

FNO RHF CCSD(T) PES for Hydrogen Fluoride

Reference

Page 18: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

*F2, HF, CO, N2, NH3, H2O – PES of symmetric dissociation

*Relative to 20% DZP Basis Calculation

Average Timings for Determination of CCSD(T) PES for Six Small Molecules* with FNO Truncation

Page 19: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Truncated Large Bases are Better than Similar-sized Small Bases

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5LOG (Relative** Time)

% C

orr

ela

tio

n E

ne

rgy

*

DZP

cc-pVTZ

cc-pVQZ

* Total Correlation Energy Determined by 100% cc-pVQZ calculation

** Times Relative to 20% DZP Calculation

Points are in increments of 20% of basis set

Page 20: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Dimethylnitramine• Model compound for RDX and HMX.• Two possible conformers:

• C2v – X-ray crystallography / gas-phase e- diffraction1;

• Cs – predicted by theory at SCF, MBPT(2), DFT, QCISD levels with moderate basis sets2. It has been argued that theoretical predictions are more accurate than experimental values.

• Dimer interactions are important to model dominant interaction in the solid phase. Given X-ray structure, best to use C2v monomer. Calculations have been done at SAPT level on fixed monomers3.

• DMNA can undergo decomposition via NO2 and HONO elimination. HONO Elimination estimated to be exothermic by ~1-3 kcal/mol at standard conditions4, therefore need high-level calculations, zero-point energy corrections, etc.These have been investigated theoretically locating transition states at the QCISD, MBPT(2) and DFT levels2.1) Stolevik, Rademacher, Acta Chem Scand 1969 23 672

2) Harris, Lammertsma, JPCA 1997 101 1370; Smith, et al., JPCB 1999 103 705; Johnson, Truong, JPCA 1999 103 8840

3) Bukowski, Szalewicz, Chabalowski, JPCA 1999 103 7322

4) Shaw, Walker, JPC 1977 81 2572

Page 21: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

DMNA Equilibrium Structure

C2v*Cs**

9.29-339.1180-339.1032cc-pVTZ – 60%

7.00 hr1.80 hrcc-pVTZ – 60% Time

9.29-339.1431-339.1283cc-pVTZ – 60% + ∆MBPT(2)

39.5 hr13.1 hrcc-pVTZ – 100% Time

9.24-339.1399-339.1252cc-pVTZ – 100%

8.91

7.66

9.09

C2v – Cs (kcal/mol)

-338.8220-338.8078DZP – 60% + ∆MBPT(2)

0.19 hr0.06 hrDZP – 60% Time

-338.8302-338.8157DZP – 100%

-338.7671-338.7549DZP – 60%

1.22 hr0.39 hrDZP – 100% Time

CsC2vCCSD(T) RHF Drop Core

Total Energies in Hartree

*Experimental geometry with HCH angles optimized at MBPT(2) Bukowski et.al. JPCA 1999 103 7322

**Theoretical prediction QCISD cc-pVDZ basis Johnson & Truong JPCA 1999 103 8840

Page 22: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

M1

M2

M3

M4

DMNA Dimer Structures† - fixed monomer geometry

† Monomer geometries are experimental methyl angles, optimized at MBPT(2) level. Dimer structures are minima of SAPT method –Bukowski, Szalewicz, Chabalowski JPCA 1999 103 7322

Page 23: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

DMNA Dimer Interaction Energies

† Bukowski, Szalewicz, Chabalowski JPCA 1999 103 7322

0

2

4

6

8

10

12

-Ein

t (k

cal/

mo

l)

M1 M2 M3 M4

SAPT Minima

SAPTThis work*

* CCSD(T) FNO 60% DZP with core occupieds dropped and ∆MBPT(2) correction

Page 24: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Background information for RDX

Decomposition Mechanisms:● NO2 Elimination: B3LYP/6-3311G** (1), DSC closed pan(liquid-like) (2)

● HONO Elimination (3)

● Triple Bond fission: IRMPD(4), DSC open pan(gas-like)(2)

● Other mechanisms: NO elimination (MALDI)(5), internal ring formation, -OH loss

Conformers of RDX:● Solid α-RDX: AAE (Cs) (6)

● Solid β-RDX: AAA● Vapor phase(e- diffraction): AAA(C3v)● Gas/liquid dynamically averaged structure(7)

The energy difference between minima is on the order of 1 Kcal/mol (B3LYP/6-311G**) with AAE being the most stable(1)

1)N. Harris, K. Lammertsma., J. Am. Chem. Soc. 119,6583 (1997)2) G. Long, S. Vyazovkin, B. A. Brems, C.A. Wight, J. Phys. Chem. B., 104, 2570 (2000)3) D. Chakraborty, R.P. Muller, S. Dasgupta, W. Goddard III, J. Phys. Chem. A., 104,2261 (2000)4) X. Zhao, E. Hintsa, Y. Lee, J. Chem. Phys., 88, 2 ,801 (1988)5) H.S. Im and E.R. Bernstein. J.Chem.Phys., 113, 18 ,7911 (2000)6)B. Rice, C. Chabalowski, J. Phys. Chem. A., 101, 8720 (1997)7) T. Vladimiroff, B. Rice J. Phys. Chem. A., 106, 10437 (2002)

Page 25: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

RDX Minima*

-1.4

-0.25

Chair-Boat

(kcal/mol)

14530CC Time (hr)

1000200Estimated Time for Full Basis (hr)

-895.3289-895.3311DZP – 60% + ∆MBPT(2)

-895.1728-895.1732DZP – 60%

AAA BoatAAA Chair

CCSD(T) RHF Drop Core

Total Energies in Hartree

*Conformations determined by B3LYP 6-31G(d) Calculations –

Chakraborty, et al JPCA 2004 104 2261

AAA ChairAAA Boat

Page 26: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Triples at a Fraction of the Cost

Compressed Coupled Cluster &

FNO CC for DMNA

CCSD(T) FNO Timings for

AAA Chair Conformer of RDX

** Estimated.

Basis Time

FNO* 60% DZP 30 hours

100% DZP 200 hours**

FNO* 60% cc-pVTZ 50 days**

100% cc-pVTZ 1 year**

FNO* 60% cc-pVQZ 2.5 years**

100% cc-pVQZ 20 years**

*FNO Speed-up ~ 8x faster with 50% truncation. For large numbers of occupied orbitals, FNO speed-up determined by o3v3 term in CCSD equations – Not by o2v4 term

CCSDT-1 RHF DZ Basis Frozen Core:

MethodCC Speed-up

Factor

Comp. CC 8.6

60% FNO CC 5.96.3

Page 27: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Transfer Hamiltonian for large clusters of molecules.

Basic idea: Represent the CC Hamitonian in itsone-particle form by a low-rank operator, that permitsrapid generation of forces for MD, but can (hopefully)retain the accuracy of CC theory, in the process.

Page 28: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

University of Florida: Quantum Theory Project

TRANSFER HAMILTONIANTRANSFER HAMILTONIAN

In CC theory we have the equations…

exp(-T) Hexp(T) = Ĥ

Ĥ|0 = E|0 Where E is the exact correlated energy

m |Ĥ|0 =0 Where m| is a single, double, triple, etc excitation which provides the equations for the coefficients in T, ie ti

a, tijab,

etc.

(R)E(R) = F(R) Provides the exact forces

(x)= 0| exp(-T)(x-x’)exp(T) |0 gives the exact density

and m| Ĥ |n Ĥ and ĤRk = kRk Gives the excitation (ionization, electron attached) energies k and eigenvectors Rk

Page 29: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

ACCURACY

1

10-2

10-4

10-6

10-8

10-10

CC

DFT

SE

TB

CPC

OS

T

COMPARATIVE APPLICABILITY OF METHODS

TH

Page 30: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

TRANSITION FROM MANY-PARTICLE HAMILTONIAN TO EFFECTIVE ONE-PARTICLE HAMILTONIAN...

Wavefunction Approach0|{i†a}Ĥ|0=0= a| Ĝ |i=0

Ĝ|i=i|i iParameterize Ĝ with a GA to satisfy E= 0|Ĥ|0,

E=F(R), (r), (Fermi) = IDensity Functional Approach

Ĝ|i=i|i i where Ĝ =t+E/(x)

and E[]=E, E=F(R), (r)= |i i|, (Fermi) = IFuture? Remove orbital dependence

and/or self-consistency?

Page 31: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Second Quantized Ĝ

Ĝ =gpq{p†q} +ZAZB /RAB

Transition from orbital based to atom based-- (hAA + AA)+ hAB(R) + AB(R)

+ Z’AZ’B /RAB{akAexp[-bkA(RAB-ckA)2] +akBexp[-bkB(RAB- ckB)2]}

hAB(R)= ( + )KS(R)

AB(R) = [( RAB)2 +0.25(1/AA+1/BB)2]-1/2

RELATIONSHIP BETWEEN COUPLED-CLUSTER/DFT HAMILTONIAN AND SIMPLIFIED THEORY

University of Florida: Quantum Theory Project

Page 32: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

aci-nitromethane

• Proper description of NMT unimolecular rearrangement is required for adequate description of combustion, detonation and pollution chemistry. • NMT is a model system for energetic materials, e.g. FOX-7, TNAZ.• NMT→ CH3∙ +NO2∙ most energetically favored, ~63 kcal/mol*.• NMT→MNT→ CH3O∙ +NO∙ second most energetically favored, ~69 kcal/mol*.• Molecular beam experiments** demonstrate NMT → MNT

nitromethane (NMT)methylnitrite (MNT)

*CCSD(T)/cc-PVTZ, Nguyen et al., J. Phys. Chem. A 2003, 107, 4286**Wodtke et al., J. Chem. Phys. 1986, 90, 3549

Nitromethane Background

Page 33: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Unimolecular Decomposition Pathways of NMT and MNT

CH3-NO2 CH3. + NO2

.

TS1 CH3ONO Rearrangement

CH3ONO CH3O . + NO.

TS2 CH2O + HNO Rearrangement

•G2MP2*•CCSD/TZP•CCSD(T)/cc-PVTZ**

* Hu et al., J. Phys. Chem. A 2002, 106, 7294** Nguyen et al., J. Phys. Chem. A 2003, 107, 4286

Energies relative to NMT

Page 34: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Nitromethane HT

Force of C-N bond breaking

-0.1

-0.05

0

0.05

0.1

0.15

1.3 1.8 2.3 2.8 3.3

R (A)

F (

H/B

oh

r) CCSD/TZP

AM1

TH-CCSD

B3LYP/6-31G*

Page 35: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Nitromethane PES for C-N rupture

-10

0

10

20

30

40

50

60

70

80

90

0.9 1.9 2.9 3.9

R_C-N (A)

En

erg

y(k

ca

l/m

ol)

CCSD(UHF)/TZP

AM1(UHF)

TH(UHF)

B3LYP/6-31G*(UHF)

Page 36: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

NMT Energy (UHF)

-10

40

90

0.9 2.9R_C-N (A)

E-E

_rel

(kca

l/mo

l)

CCSD(UHF)/TZP

MNT Energy

-10

40

90

0.9 2.9R_C-O (A)

E-E

_rel

(kca

l/mo

l)

CCSD(RHF)/DZP

aci-NMT Energy

-10

40

90

0.9 1.9R_C-N (A)

E-E

_rel

(kca

l/mo

l)CCSD(RHF)/TZP

NMT Energy (RHF)

-10

40

90

0.9 2.9R_C-N (A)

E-E

_rel

(kca

l/mo

l)

CCSD(RHF)/TZP

Reference Data

Page 37: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Nitromethane Clusters

• Our nitromethane dimer and trimer calculations used local minima found by Li, Zhao, and Jing in their application of BSSE corrected DFT/B3LYP with 6-31++G** basis*. This reference also concludes that a proper description of three body effects is needed for accurate determination of potential energy surfaces for bulk nitromethane.

• The most stable dimer configuration was that in which two hydrogen bonds of length 2.427Å are formed while trimer involved a ring structure in which the three hydrogen bonds of lengths 2.329Å, 2.313Å, and 2.351Å. This configuration for the dimer minimum is also supported by CP corrected SDQ-MBPT/DZP in which the hydrogen bonding distance is found to be 2.25Å**.

• With TH-CCSD we observe the formation of methoxy radical in the dimer and the formation of methylnitrite in the trimer, similar to predicted unimolecular mechanisms found at the G2MP2/B3LYP/6-311++G(2d,2p) level of theory ***.

* J. Li, F. Zhao, and F. Jing, JCC 24 (2003) 345.** S. J. Cole, K. Szalewicz, G. D. Purvis III, and R. J. Bartlett, JCP 12 (1986) 6833. S. J. Cole, K. Szalewicz, and R. J. Bartlett, IJQC (1986) 695.*** W.F. Hu, T.J. He, D.M. Chen, and F.C. Liu, JPCA 106 (2002) 7294.

Page 38: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Breaking of H-Bonds in Nitromethane Dimers with Frozen Monomers

SAPT equilibrium OH distance*

Page 39: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Nitromethane Decomposition in DimerH3CNO2

* + H3CNO2 H3CNO + H3CO + NO2

UHF TH-CCSD predicts thatrearrangement

occurs when C-N bond is 2.42 Å

UHF AM1 prediction

* Indicates bond rupture

Page 40: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Nitromethane Rearrangement in TrimerH3CNO2* + 2 H3CNO2 3H3CONO

UHF AM1 prediction

* Indicates bond rupture

UHF TH-CCSD predicts thatrearrangement

occurs when C-N bond is 1.94 Å

Page 41: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

0

0.5

1

1.5

2

2.5

3

% e

rro

r fr

om

CC

SD

/TZ

P

R_CH R_CN R_NO AHCN AONC

Property

TH/CCSD

AM1

Equilibrium Geom of NMT

Page 42: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Force of C-N bond breaking

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

1.3 1.8 2.3 2.8

R (A)

F (

H/B

oh

r)

B3LYP/6-31G

AM1

TH-CCSD

TNAZ C-N Bond Rupture

*C-N bond breaking trans to N-NO2

Page 43: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

SUMMARY

•Derived and illustrated the NO-CC methodwith applications to DMNA and RDX. Savings is ~7 out of theoretical 16. With rapid processors, will make state-of-the-art CC resutls possible ina week, instead of a year.

•Awaiting analytical gradients (programmed) to enable geometry and transition state searches.

•Illustrated tranfer Hamiltonian approach to retain the accuracy of CC theory, but for much more complicated representations of the condensed phase.

•Establsihed rigor of the theory. We are working on alternative,and better realizations of the concept.

Page 44: ARMY RESEARCH OFFICE Military University Research Initiative  Oct 16, 2003

Energy of N-N bond breaking

-20

0

20

40

60

80

100

1.1 1.6 2.1 2.6 3.1

R (A)

(E-E

eq)

(kca

l/m

ol)

CCSD(T)/cc-PVTZ

B3LYP/6-31G*

⇒ Forces from DFT are qualitatively and quantitatively wrong at non-equilibrium geometries!

Nitramine: Dangers of DFT