Polyspherical Description Polyspherical Description of of a N-atom system a N-atom system Christophe Iung LSDSMS, UMR 5636 Université Montpellier II e-mail : [email protected]Collaboration avec Dr. Fabien Gatti, Dr. Fabienne Ribeiro et G. Pasin Pr. Claude Leforestier (Montpellier) Pr. Xavier Chapuisat et Pr. André Nauts (Orsay et Louvain La Neuve)
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Polyspherical Description of a N-atom system Christophe Iung LSDSMS, UMR 5636 Université Montpellier II e-mail : [email protected] Collaboration avec.
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V’ « extrapotential term » that depends on the masses. It can be treated with the potential
This formulation has be exploited by E.L. Sibert et coll. in hisCVPT perturbative formulation: J. Chem. Phys., 90, 2672 (1989)
Ideal features of a KEO expressionIdeal features of a KEO expression
Compact Expression of the KEO : larger is the number of terms, larger is the CPU time
Use of a set of coordinates adapted to describe the motion of atomsin order
*to reduce the coupling between these coordinates
* to define a working basis set such that the Hamiltonian matrix is sparse
The numerical action of the KEO must be possible and not too much CPU time consuming
The expression should be general and should allow to treat a largevariety of systems
2- Polyspherical Parametrization
The N-atom system is parametrized by (N-1) vectors described by their Spherical Coordinates ((Ri,i, i), i=1,...,N-1)
The General Expression of the KEO is given in terms of either
1- the kinetic momenta associated to the vectors
And the (N-1) radial conjugate momenta pRi
===> adapted to the description of large amplitude motion
OR
2- the momenta conjugated with the polyspherical
coordinates ((Ri,i, i),i=1,...,N-1)
===> adapted to the description of highly excited semi-rigid systems
(pRi, p i
, p i)
= -i
Ri
Development of this parametrizationFirst description of its interest :
X. Chapuisat et C. Iung , Phys. Rev. A,45, 6217 (1992)
Review papers : F. Gatti et C. Iung,J. Theo. Comp. Chem.,2 ,507 (2003) et
C. Iung et F. Gatti, IJQC (sous presse)
Orthogonal Vectors : F. Gatti, C. Iung,X. Chapuisat JCP, 108, 8804 (1998), and 108, 8821 (1998)
M. Mladenovic, JCP, 112, 112 (2000)
NH3 Spectroscopy : F. Gatti et al , JCP, 111, 7236, (1999) and 111, 7236, (1999)
Non Orthogonal Vectors : C. Iung, F. Gatti, C. Munoz, PCCP, 1, 3377 (1999) M. Mladenovic, JCP, 112, 1082 (2000);113,10524(2000)Semi-Rigid Molecules : C. Leforestier, F. Ribeiro, C. Iung 114,2099 (2001) F. Gatti, C. Munoz and C.Iung : JCP, 114, 8821 (2001) X. Wang, E.L.Sibert and M. Child : Mol. Phys, 98, 317(2000)
H.G Yu, JCP,117, 2020 (2002);117,8190(2002)
HF trimer : L.S. Costa et D.C. Clary, JCP, 117,7512 (2002)Diatom-diatom collision : E.M. Goldfield,S.K. Gray, JCP, 117,1604(2002) S.Y. Lin and H. Guo, JCP, 117, 5183(2002)
““ORTHOGONAL” SET OF VECTORSORTHOGONAL” SET OF VECTORS
Polyspherical Coordinates :R3, R2, R1,
1,
et out-of-plane dihedral angle)
BF GzH H
Jacobi Vectors Radau Vectors
O OC C
F H
i i
i iPP
T
2
Non Orthogonal Set of VectorsNon Orthogonal Set of Vectors
Polyspherical Description : R3, R2, R1, 1, and
- M matrix determination M (Trivial) - Dramatic Increase of term number… CPU can dramatically increase
2T
P i
P jMiji, j
Valence Vectors
BF Gz
OCH
H
Determination de la Matrice MDetermination de la Matrice M
Any set of vectors can be related to a set of Jacobi vectors :
R A
r Jacobi M = At A
if 2T
(P i
Jac ) P i
Jac
ii
P i
P jMiji, j
La Matrice M est une matrice très facile à déterminer et dépendant des masses
Elle permet de généraliser les résultats obtenus avec les vecteurs orthogonaux
Developed expressions of the KEO
*kinetic momentum Li
associated with Ri and the radial momenta
*Conjugate radial and angularmomenta
(L i , P iR = - i
Ri
)
By using Obtained by the
substitution of the angular momentum
P i =
PiR R i
Ri
+
L i
R i
Ri2
* Lix - sin i pi cos i p
i
* Liy cos i pi sin i p
i
* Liz pi
A BF (Body Fixed) frame has to be defined to introduce the total angular momentum (full
rotation) vector J
{
by dsubstitute is ; from Starting ic PPMPT
2
P
iR = - i Ri
, Pi = -i
i
, Pi
= - i i
Choix du Body Fixed
The (Gz)BF is chosen parallel to RN-1 ; LN-1 is substituted by
This requires 2 Euler rotations ()
The last Euler rotation ( can be chosen by the user
In general, RN-2 is taken parallel to the plane (Gxz)BF
But other choice can be done :N atoms = 3N-3 degrees of freedom
By taking into account the fact thatBy taking into account the fact thatRRN-1N-1 and R and RN-2 N-2 are linked to the BF frameare linked to the BF frame
(problem of no-commutation of the operator(problem of no-commutation of the operator that depends on vectors Rthat depends on vectors RN-1N-1 and R and RN-2 N-2 ))
It results in general expression of the KEOIt results in general expression of the KEO
with
One finds that :
The problem of no-commutation are such that
KEO developed expression for a system describedby a set of (N-1) orthogonal vectors
KEO developed expression for a system describedby a set of (N-1) orthogonal vectors
General Expression of TGeneral Expression of Tc c in terms of the conjugate momentain terms of the conjugate momentaAssociated with the polyspherical coordinates Associated with the polyspherical coordinates Expression used to study semi-rigid systemsExpression used to study semi-rigid systems
F. Gatti, C. Munoz, C. Iung, JCP, 114, 8821 (2001)F. Gatti, C. Munoz, C. Iung, JCP, 114, 8821 (2001)
The expression of the KEO are known…The expression of the KEO are known…How can we use them How can we use them
for instance for semi-rigids systems ?for instance for semi-rigids systems ?
1- Orthogonal Coordinates provides rather simple expression of KEO…
However, these coordinates does not necessary describe a real deformation of the system
2- Interesting coordinates, such valence coordinates, are not ‘orthogonal’ The KEO expression is intricate
Two sets of coordinates can be used…This is the idea of the Jacobi-Wilson Method
Definition of “Curvilinear Normal Coordinates”,Qi, In terms of polyspherical coordinates qj :
Hvib0
1
2(qnFn,m
n ,m
3N 6
qm pnGn ,m0 pm ) Gn ,m
0 G(qeq ) Fn,m 2V
qnqm
qeq
where and
QL 1qPolysphericalCoordinates
Normal ModesDefined in terms of
Polyspherical coordinates
Advantages : Simplicity of Tc in terms of polyspherical coordinates
Physical Interest of the Normal Modes
Jacobi-Wilson Method(C. Leforestier, A. Viel, C. Munoz, F. Gatti and C. Iung, JCP, 114, 2099 (2001))
Pq is substituted by (tL) PQ in Tc
JACOBI-WILSON STRATEGYJACOBI-WILSON STRATEGY
H
Jacobi Vector
OC
F
• Description Polyspherique
• Simple Expression of the KEO T JACOBI
• Normal Mode Coordinates :
• Definition of a working basis set :
WILSON
1...3N 6
qLQ 1
H H 0 V T
DIAGONALIZATION
Application to HFCO et H2CO Up to10000 cm-1
Improvement of the zero-order basis setImprovement of the zero-order basis set
On can take into account to the diagonal anharmonicity:
Hvib
0, 2
2
2
2Q V (Q )QQeq
H H 0 V T
m
N
mnmnmn
n
anharm
qGG
qT
VVV
)(2
63
,
0,,
2
H Matrix calculationH Matrix calculation
q
semi-analytical estimation of its action
VG
pseudo spectral scheme used
Spectral Representation :
Grid Representation:
(Q1...Q6 ) n1 ...n6n1
(n1...n6
Q1)...n6(Q6 )
(Q1a ...Q6 f ) n1 ...n6n1
(n1...n6
Q1a )...n6(Q6 f )
Ideal features of a method that provides Ideal features of a method that provides eigenstates and eigenvalues which can be locatedeigenstates and eigenvalues which can be located
in a dense part of the spectrumin a dense part of the spectrum
•Application to a large variety of systems ;
•Use of huge basis set ;
•Obtention of eigenvalues and eigenstates;
•Control of the accuracy of the results ;
•Small CPU time, Small memory requirement ;;
•Easy to use and to adopt ;
•Specific Calculation of energies in a given part of the spectrum ;
Iterative Construction of the Krylov subspace generated by {un, n=O,N} :
1- Initialization : A first guess vector u0 is chosen
2- Propagation : The following vector un+1 is calculated
n+1 un+1 = (H – n) un – n un-1
with
n = <un|H|un>
n+1= <un+1|H|un>
LANCZOS METHODLANCZOS METHOD
• Lanczos Method:
0
BNB
N
H
dimdim
0211
10
dim
LANCZOS FEATURESLANCZOS FEATURES
• Avoid the determination of the full H matrix.• The convergence is slower when the state density
increases
DIAGONALISATION DE HDIAGONALISATION DE H
Diagonalisationdirecte
Méthode de
Lanczos
Ouverture de Fenêtres en
énergie
E0
0
50
100
150
200
250
300
0 5000 10000 15000
Energies en cm-1
r (
po
ur
10
0 c
m-1
)
• Spectral Transform . Lanczos applied to G=(Eref°-H)-1. or exp(-(H-Eref)2)
One has to open some window energyOne has to open some window energy
Modified Block-Davidson AlgorithmModified Block-Davidson Algorithm to to calculate calculate
a set of a set of b coupled eigenstatesb coupled eigenstates
Method based on one parameter : Method based on one parameter : which sets the accuracy which sets the accuracyF. Ribeiro, C. Iung, C. Leforestier JCP in pressF. Ribeiro, C. Iung, C. Leforestier JCP in press
C. Iung and F. Ribeiro JCP in pressC. Iung and F. Ribeiro JCP in press
The working basis set Banh is divided into : Banh = P° Q .
Where P° contains the zero-order states which play a significant rôle in the calculation performed :
H is diagonalized in P°, et this new basis set {u°i ,E°i } is used during the Davidson scheme
E°1
E°i
Eanh1
Eanhq
0
0
0
0
0
0
P°
Q
H°H°==
Prediagonalization step in order to reducePrediagonalization step in order to reducethe off-diagonal termsthe off-diagonal terms
We can defined the block of states using the second-order perturbation
00002
,
EE
uHu
EE
uHu q
Qq q
q
States such that are retainedun a given block :
1.02,
Determination of the Block of statesDetermination of the Block of states
• Faible barrière de dissociation (14000 cm-1)
HFCO HF + CO
• Mode de déplacement hors du plan très découplé à haute énergie.
• Forte densité d ’états
APPLICATION TO HFC0APPLICATION TO HFC0
Selectivity of the energy transfer in HFCOwhose out-of-plane mode is excited
Moore et coll. have studied the highly excited out-of-plane overtones (nout-of-plane, n=14,…,20) :
they predict the localization of energy in these states
How can we understand that a highly excited state can be localized in one mode
while the state density is large for Eexc=14000-20000cm-
• Between 1 and 60 Davidson iterations are required to calculate each state.E is not a correct indicator of the convergence
Davidson Iteration Number
-État 60-État 120-État 180
Lan
czo
s
CONVERGENCE OF THE DAVIDSON SCHEMECONVERGENCE OF THE DAVIDSON SCHEME
Nombre d ’itérations Davidson
ErrorOn theEnergy (cm-1)
• I : IIq(M)IImax < 10 cm-1
Pour E < 0.01 cm-1
IIq(M)IImax < 50 cm-1
Pour E < 0.5 cm-1
Convergence criterionConvergence criterion
Davidson Iteration Number
Err
eur
(cm
-1)
)()( )ˆ( Mr
MrM MM
HEq
• IIq(M)II constitue an excellentIndicator of the convergenceAnd the accuracy of the eigenenergy and eigenstate.
Numerical CostNumerical Cost
0
1000
2000
3000
4000
5000
6000
7000
8000
2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
BLOC-DAVIDSON
LANCZOS
Nombre d ’actions de H
Energie d ’excitation (cm-1)
Determination of an Active Space specificaly Determination of an Active Space specificaly built to study a given statebuilt to study a given state
Example : state |106> in HFCO
(State n° 1774, in a 100,000 state primitive basis setCaracterized by vmax(in plane)=8 and Emax=32,000cm-1)
We begin with a Davidson calculation performedon |106>(0) in a 7,000 state basis set defined by vmax(in plane)=4 and Emax=24,000cm-1
The Davidson scheme in this small basis set converges andprovides an estimation of the eigenstate studied: |106>(1)
The largest |v1,…,v6>°contributions of this estimated eigenstate |106>(1) are retained
in a small (368 states) « active space » Po used in the calculation in the large (100,000 states) basis set
6 8 10Zero Order Energy 6439.6 8641.9 10849.9 P0 dimension
1 1 368 Prediagonalized Energy of the guess
6439.6 8641.9 10127.1 Converged Energy 6018.4 7984.9 9948.8 Overlap with the guess
0.77 0.64 0.92 Main Contributions of the eigenstate
+0.77 6 +0.28(
+ 0.64 8 0.30(
0.31 + 0.51 10
v1averaged 0.27 0.47 0.69
v2averaged 0.08 0.11 0.17
v3averaged 0.14 0.31 0.37
v4averaged 0.06 0.20 0.15
v5averaged 0.02 0.23 0.04
v6averaged 5.47 6.75 8.57
Application to the calculation of highly Application to the calculation of highly Excited overtones in HFCOExcited overtones in HFCOState 10State 1066: State n°1700: State n°1700
Similar coefficientsobtained for different
overtones :The nature of the
couplingis identical
for these overtones
The CH stretch is the more
coupled mode
CH stretch
HCO bend
Main features of this newMain features of this new Prediagonalized Block-Davidson SchemePrediagonalized Block-Davidson Scheme
•It can be coupled to any method which can provide the action of the
Hamiltonian on a vector
Huge basis set can be used (more than 100 000 states)
•Calculation of the eigenstates and eigenenergies
•The accuracy of the results can be controled (with ||qM||)
•Low memory cost
•Faster and more efficient than Lanczos
•Very easy to use because it depends only on one parameter •It is adapted to calculate a series of coupled states
Conclusions
The development of a general method to calculate high excited ro-vibrational state is crucial Different approachs have to be exploited :
• The Jacobi-Wilson method coupled with the Davidson algorithm presents interesting
advantages.
•It allows the specific calculation of eigenstates associated with highly excited states
It can be improved by using a MC-SCF or SCF treatment
• However a lot of work has to be done… improve the fit of V, use a fit of the KEO in order to reduce