Time-dependent Hartree Fock with full Skyrme Forces in 3 Dimensions
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Transcript of Time-dependent Hartree Fock with full Skyrme Forces in 3 Dimensions
Time-dependent Hartree Fock with full Skyrme Forces in 3 Dimensions
Collaborators:
P.-G. Reinhard, U. Erlangen-Nürnberg
P. D. Stevenson, U. Surrey, Guildford
TopicsThe codeQualitative explorationsEnergy loss in 16O+16O:
Effect of full Skyrme and 3DThe spin excitation mechanismAccuracy of relative motion energy
TDHF in the late `70s
Computer facilities: The 3D code was run on an IBM „supercomputer“ 360/195 with 1MB of memory!
Therefore: no spin, simplified interaction: BKN or g-matrix
Really very few checks of accuracy (!?) R.Y. Cusson and J.A. Maruhn, „Dynamics of 12C + 12C in a Realistic T.D.H.F. Model“, Phys. Lett.
62B, 134 (1976). R.Y. Cusson, R.K. Smith, and J.A. Maruhn, „Time-dependent Hartree-Fock Calculation of the
16O+16O Reaction in Three Dimensions“, Phys. Rev. Lett. 36, 1166 (1976). J.A. Maruhn and R.Y. Cusson, „Time-Dependent Hartree-Fock Calculation of 12C + 12C with a
Realistic Potential“, Nucl. Phys. A270, 471 (1976). R.Y. Cusson, J.A. Maruhn, and H.W. Meldner, „Direct Inelastic Scattering of 14N+12C in a Three-
Dimensional Time-Dependent Hartree-Fock Scheme'', Phys. Rev. C18, 2589 (1978). C.Y. Wong, J.A. Maruhn, and T.A. Welton, „Comparison of Nuclear Hydrodynamics and Time-
Dependent-Hartree-Fock Results“. Phys. Lett. 66B, 19 (1977).
The New TDHF Code
Three-dimensional Skyrme-force Hartree-Fock, both static and time-dependent
Differencing based on Fast-Fourier-Transform; Grid spacing typically 1 fm All variations of modern Skyrme forces can be
treated fully Fourier treatment of Coulomb allows correct
solution for isolated charge distribution Coded fully in Fortran-95 TDHF version can run on message-passing
parallel machines
The Skyrme Energy Functional
Fourier calculation of potential for isolated charge distributions
(fictitious) empty space
The solution constructed via
with two FFToperations in the enlarged region with periodic boundary conditions fulfills the boundary condition for an isolated charge distribution in the physical region
J.W. Eastwood and D.R.K. Brownrigg, J. Comp. Phys. 32, 24 (1979)
2
4( ) ( )V k k
k
The wave functions have periodic boundary conditions, but for the Coulomb filed interaction with images must be avoided
16O+48Ca slightly below barrier
16O+48Ca slightly above barrier
16O + 48Ca, Boost 0.3 MeV / nucleon, t=0..450 fm/c
16O + 48Ca, Boost 0.3 MeV / nucleon, t=500..950 fm/c
Mass Moments in 16O+48Canormalized to initial value
0 100 200 300 400 500 600 700 800 900 1000
t [fm/c]
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Q /
Qin
it
MomentQ2Q3Q4
Heavy Systems: 48Ca+208PbImportant for Superheavy Element Formation!
Does the interaction dynamics differ dramatically from light system?
12 fm initial distance 4000 time steps of 0.25 fm/c : 1000 fm/c total Initial boost just sufficient to cause interaction Needs longer times and systematic variation in boost
48Ca + 208Pb sligtly above barrier
48Ca+208Pb near barrier, t=0..450 fm/c
48Ca+208Pb near barrier, t=500..950 fm/c
Mass Moments in 48Ca+208Pbnormalized to initial value
0 100 200 300 400 500 600 700 800 900 1000
t [fm/c]
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
Q /
Qin
it
MomentQ2Q3Q4
Deformed partners: 20Ne+20Ne
A curious case: 12C+16O
Energy Loss in 16O+16O
Past experience shows that relaxing symmetries increases the dissipation
Spin orbit coupling is essential for correct shell structure!
Few calculations performed at that time show increased dissipation due to relaxation of symmetries
Now examine energy loss aspects in new directions:• Accuracy• Effect of 3-D and full modern Skyrme forces• Role of time-odd parts in the s.p. Hamiltonian
Changes in results The dissipation is generally increased when
symmetries are relaxed and new degrees of freedom enter
A.S. Umar, M.R. Strayer, and P.-G. Reinhard, Phys. Rev. Lett. 56, 2793 (1986).
Translational Invariance of T.D.H.F.
A ground state nucleus with s.p. wave functions fulfilling
leads to a propagating stationary solution with a common phase factor
This solves the time-dependent equation (i.e., produces a uniformly translating nucleus), if the s.p. Hamiltonian is Galilei invariant
This is trivial for pure density dependence, but requires adding terms involving currents and spin currents to the density functional(Y. M. Engel, D. M. Brink, K. Goeke, S. J. Krieger, and D. Vautherin,
Nucl. Phys. A249, 215 (1975)).
/( ) i tr e
22 ( { }) ( ) ( )
2V r r
m
exp[ ]k
ik r r tm
The time-odd spin-orbit terms in themean-field Hamiltonian
In the Skyrme energy functional Galilei invaraince requires adding terms like
and similar terms with different isospin dependence. This leads to contributions in the mean-field Hamiltonian like
with
The spin-orbit part of these contributions was usually neglected (and is negligible for giant-resonance-type calculations)
Determination of relative motion energy
Find minimum of density alongaxis of largest moment of inertia
If density is low enough, definedividing plane
Determine c. m. distance Rof fragments and ist time derivative
Get relative motion kinetic energy from
for central collisions
Point-charge Coulomb energy agrees with full calculation toabout 0.02 MeV
Accuracy in „trivially“ conserved quantities: total energy 0.1 MeV, particle number 0.01
22 1 2
2cm
Z Z eE R
R
Initial Relative Motion Energy
2 4 6 8 10 12 14 16
R [fm]
20
40
60
80
100
120
140
Ecm
[M
eV]
time-odd termswithwithout
Omission of time-odd l*s terms leads to translational noninvariance of surprisingly strong consequences!
Importance of Time-Odd L*S-Termsin Central 16O+16O Collisions
75 100 125 150
Ecm [MeV]
0
10
20
30
40
50
60
70
80
90
Efi
na
l [M
eV
] Sly6
75 100 125 150
Ecm [MeV]
0
10
20
30
40
50
60
70
80
Efi
na
l [M
eV
] SkI3
75 100 125 150
Ecm [MeV]
0
10
20
30
40
50
60
70
80
Efi
na
l [M
eV
] SkI4
75 100 125 150
Ecm [MeV]
0
10
20
30
40
50
60
70
80
90
Efi
na
l [M
eV
] SkM*
The Mechanism
L*S Energy in Central Collision
0 50 100 150 200
-6
-4
-2
0
2
4
6
8
10
12
od
d-o
dd
l*s
en
erg
y [M
eV
]
t [fm/c]
0 50 100 150 200
-6
-4
-2
0
2
4
6
8
10
12
od
d-o
dd
l*s
en
erg
y [M
eV
]
t [fm/c]
Impact Parameter Dependence
0 50 100 150 200
-8
-6
-4
-2
0
2
4
6
8
10
12
SkM*
Ecm
=100 MeV
Od
d-o
dd
sp
in o
rbit
en
erg
y [M
eV
]
t [fm/c]
b [fm] 0.0 1.6 3.2 4.8 6.4 8.0
Force dependence of reactions: a dynamic test for Skyrme forces
J. A. Maruhn, K. T. R. Davies, M. R. Strayer, Phys. Rev. C31 1289 (1985)
0 1 2 3 4 5 6
t [10-21s]
6.5
7
7.5
8
8.5
9
9.5
Rrm
s [f
m]
ForceSkVISkVSkIVSkIIISkII
86Kr + 139La
Elab = 370 MeV
Comparison with previous results
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
0
10
20
30
40
50
60
70
80
90
Efin
al [M
eV
]
Ecm
[MeV]
old, no l*s old, with l*s SkI3 SkI4 Sly6 SkM*
Noncentral Results at Ecm=100 MeV
-1 0 1 2 3 4 5 6 7 8 9 10
0
20
40
60
80
100
Efin
al [M
eV
]
b [fm]
SkM*, odd l*s SkM*, no odd l*s SkI3, odd l*s old, no l*s old, with l*s
Late-time behavior shows severe problem!
12 12.5 13 13.5 14 14.5 15 15.5
R [fm]
25
26
27
28
29
25
Ecm
[M
eV]
50
51
52
53
54
5555
56
57
58
59
6060
50
55
60
Ecm
[M
eV]
time-odd termswith
without
Use new plot
10 12 14 16 1826
27
28
29
30
31
32
124
125
incoming
Ecm
[M
eV]
R [fm]
small mesh: 242x32
larger mesh: 322x48 absorption layer
Problem : Pairing
Without pairing, the deformations are still not quantitative and the moments of inertia will be wrong, unless pairing is destroyed rapidly (?)
“Old” calculations did not include pairing, because the BCS formalism with state-independent pairing matrix element produces interaction even between separated fragments
Newer formulations of pairing generate matrix elements from a force such as a -pairing
The solution of the time-dependent Hartree-Fock Bogolyubov problem therefore may have to be attempted
Conclusions
The use of full Skyrme forces brings surprising new effects and problems.
The is a new energy loss mechanism involved with a „spin-twist excitation“
There are problems with a continued loss of relative motion energy for separated fragments, possibly due to cross-boundary interactions. More computational expense may be needed or one has to live with 3 MeV uncertainty.
The energy loss appears to stabilize for several forces It will be interesting to see how these effects persist in heavier
systems.