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HAL Id: jpa-00246799

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The Crumpling Transition of Dynamically Triangulated Random Surfaces

Christian Münkel, Dieter Heermann

To cite this version:

Christian Münkel, Dieter Heermann. The Crumpling Transition of Dynamically Triangulated Random Surfaces. Journal de Physique I, EDP Sciences, 1993, 3 (6), pp.1359-1370. �10.1051/jp1:1993184�.

�jpa-00246799�

(2)

Oassification Physics Abstracts

05.90 64.60A 64.60F 68.10 87.20C 12.90

The Crumpling Transition of Dynamically Wiangulated Random Surfaces

Christian Mfinkel and Dieter W. Heermann

(~) Institut fur theoretische Physik, Universitit Heidelberg, Philosophenweg 19, 6900 Heidelberg, Germany

(~) Interdisziplinires Zentrum fur wissenschaftliches Rechnen der Universitit Heidelberg, 6900

Heidelberg, Germany

(Received

2 February J993, accepted 9 February

1993)

Abstract. We present the crumpling transition in three-dimensional Euclidian space of dynamically triangulated random surfaces with edge extrinsic curvature and fixed topology of

a sphere as well as simulations of a dynamically triangulated torus. We used longer runs than previous simulations and give new and more accurate estimates of critical exponents. Our data indicate a cusp singularity in the specific heat. The transition temperature, as well as the exponents are topology dependent.

1. Introduction.

In this paper we are concerned with the statistical mechanics of surfaces. A

possible approach

in space dimensions D > I is to discretize the surface

using

a

triangulation [1-4].

For this

we need to

specify

the Hamiltonian 7i. The surface S is

replaced by

a

simplical triangulation T, specified by

the number of nodes N, of links and

triangles,

and the X-coordinate field

by

the coordinates X of the nodes, The metrical fluctuations of the manTold are modeled

by summing

over

triangulations

induced

by link-flips [5-7].

The Hamiltonian is now

choosen,

such

that the

partition

function is not dominated

by configurations

with

spikes.

In order to surpress these

spikes

one adds a term with extrinsic curvature. As a function of the extrinsic curvature the model shows a transition

(crumpling transition)

at finite

rigidity

of the surface

[8-18].

In a

previous

paper, we discussed the extrinsic and intrinsic

geometrical properties

of

dynamically triangulated

random surfaces

(for example

the

Hausdorff-dimension, spectral

and

spreading dimension) above,

below and at the transition

[32].

The

partition

function of the above model can be written as

ZN "

jd~Xo j ~~ fl d~X;e~'~ (1)

(3)

where the translational mode is

integrated

out. The Hamiltonian 7i is defined a8

N

~ =

p, (

(xi xj)2

+ >

£ (i

na,

nb>)

"

~

~°~ " ~~~

ii,)) ~

,

.>~J

~ fi

7i~ ~

The Gaussian part of the Hamiltonian

zig

is a sum over the

positions

X in

embedding

Euclidian space of all nearest

neighbour nodes,

I-e- all links of the

triangulation.

We shall use

fl

= I

because of the

rescaling

invariance.

7ie is an

edge

extrinsic curvature term

[19-26]. £~

~ denotes a summation over all

adjacent triangles

which share an

edge

and na, na, is

the"scilar product

of the

vectors normal to a

triangle.

The third part of the Hamiltonian 7im is the discretization of the square root of the metric.

a; denotes the number of nearest

neighbours

of node I. a

depends

on the measure. We used

a =

D/2

for the simulations in D = 3 dimensional

embedding

space.

Here we

investigate

such a model

numerically (Monte

Carlo

simulations), applying

finite-size

scaling

ideas. These ideas have proven successful in other contexts for the

analysis

of

phase

transitions. We expect that the above model shows a

phase

transition at some critical value of the

coupling

I. There are several

questions

which we want to address: What is the order of the transition? If the transition is of second

order,

what are the

exponents?

Are the exponents

topology dependent?

Is the transition temperature

topology dependent?

2. Simulation Method and Autocorrelations.

First let us

study

the effect of the extrinsic curvature on the autc-correlation time of several

observables,

I-e-, we are interested in the

dynamics

of a random surface induced

by

a Monte Carlo process. Such a

study

is of course a

prerequisite

for a detailed numerical

study

of the

apparent transition which such surfaces

undergo

as a function of a

bending rigidity.

From our results which we present below we must conclude that extensive computer resources must be

applied

because of the very

long

relaxation times which even for moderate surface sizes can

reach several tenthousand sweeps.

We want to look at the closed

dynamically triangulated

random surfaces without self- avoidance. As models for such surfaces we take the first two

topologically

closed surfaces:

The

sphere

and the torus

(cf. Fig. I).

The torus is

specified by identifying edges

of the pa-

rameter space P whereas the

sphere,

because of its genus needs a

slightly

more

complicated

set-up

procedure.

What we are interested in is to calculate the autc-correlation function of an observable O as

a function of time

~°~~'~~

~

~~~~i~~< I$(~~

~ ~~~

and its

dependence

on the number of nodes N of the surface. From the autc-correlation function we are then able to extract the autc-correlation time To

(N).

This is done

calculating

the

integrated

autc-correlation

function,

I-e-,

+OJ tint,O "

j j

d~ PO (~i

N) (4)

-OJ

We also

compared

the

integrated

autc-correlation time with the

exponential

correlation time and the statistical

inefficiency,

but found no

disagreement

within the errors. If the

successively

(4)

Fig-I-

Shown are two examples of configurations of dynamically triangulated random surfaces.

The left picture shows a sphere and the right part a torus.

generated configurations

can be considered as

non-interacting

beads as is done in the Rouse

theory [27,

28] we will find for

example

for the radius of

gyration

rR» c~ N

(5)

syr

and in

general

we expect

To cc N~

(6)

To calculate observables such as the

gaussian

part

zig

of the Hamiltonian or the radius of

gyration Rgyr,

we use the standard Monte Carlo

algorithm [29-31].

Such an

algorithm

induces a stochastic

dynamics

and all our results

apply only

to such an induced

dynamics.

One Monte Carlo sweep is

completed

when each

triangulation point

was

given

the chance for a

displacement

from its

previous position

and the

edges

of the

triangulation

were

given

the chance to re-connected or

flip

to an

orthogonal position (cf. Fig.

2. The

flip operation implements

the

sum over all

possible triangulation).

This

corresponds

to one new

configuration.

Fig.2.

This figure demonstrates the elementary moves which are made during one update of a

triangulated random surfaces.

Table I summarizes our results for the exponent a for the

sphere.

The exponents where extracted from the data of system sizes from 36 up to 288. At this

point

we should mention that the

expected

transition is at

lc

cS I-S- Out data was collected above and below the

transition.

(5)

Above and below the transition the radius of

gyration

shows the Rouse behaviour. The Gaussian part of the Hamiltonian shows

clearly

a

dependence

on the

bending rigidity.

Above the transition

point

the autc-correlation exponent

changes

to one and below it is almost zero.

The same holds for the

edge

part of the Hamiltonian.

Table I. Table

of

the results

for

the exponent a on the auto-correlation times

of dynamically triangulated

random

sphere.

I is the measure

of

the

bending rigidity. Skiff

and

flips give

the acceptance

probability for

a

displacement of

a node and

flip for

an

edge change.

r rate

0.00 0.2+0.3 0.2+0.2 1.1+0.2 0.51 0.76

1.75 1.0 + 0.1 0.8 + 0.2 1.1 + 0.2 0.47

+

Almost all of the observations for the

spherical

case carry over to the case of the torus.

3. Results of the Simulations.

Finite size

scaling

assumes, that there is

only

one relevant linear

length scale,

which is com-

pared

to the correlation

length.

To

apply

finite size

scaling

to the

crumpling

transition of

dynamically triangulated

random surfaces

(DTRS)

one must therefore assume a

single length

scale determined

by

the number of nodes N and the internal dimension d of the surface

L cc

N"~ (7)

This internal dimension d also

depends

on the external

properties

of the surface and 1

[32].

So let us first look at the

specific

heat. If the transition is of second order we would have

C(I, L)

=

L°'"i~ ((I lc)L~"] (8)

where

t~

is

a

scaling function,

which

depends

on how one

implements

the surface. At the critical I the

scaling

function is

regular

and the

scaling hypothese

leads to

Cj$~

c~

AN°'"~

+

(9)

for the

scaling

of the

peak

in the

specific

heat. If we assume a first order transition then Cj$~~

diverges

as

L~

because of the b-distribution of

Ccc (T) [33, 35].

An evaluation of the

specific

heat C of DTRS

(neglecting

the metric contribution

7im) gives

the

following expression

Call " +

~ (< 7il

> < 7ie

>~) (lo)

The first part is related to the Gaussian Halniltonian

zig

and the second to the

specific

heat C of the

edge

extrinsic curvature 7ie. The

specific

heat for the

edge

extrinsic curvature is shown

(6)

in

figure

3 for the two

topologies

considered. The

interpolation

was done

by

the method of

Ferrenberg

and Swendsen [36, 37]

using histograms

of 7ie

6 6

36 -

~~

64 - s -

64 --

5 108 --

100 -- 144 --

144 -

288 - 4

196 -

4

432 -

256 -

400 -

~ 3

2 2

0 0

O-S I I-S 2 2,5 3 O-S I I-S 2 2.5 3

~ ~

Fig.3.

Specific heat c

(edge

extrinsic curvature

part)

of the sphere

(left part)

and of the torus

(right part),

6

5.5

~

# 5

~- ~-

~iZ 4.5

#

E

4 torus --

sphere --

3,5

3

50 100 150 200 300 400500

N

FigA.

Maximum of the specific heat cfl~~ of the torus

(o)

and the sphere

(D).

Using

the data of the

specfic

heat obtained

by applying

the

extrapolation method,

we can

get

a very accurate estimate of the

positions

of the maxima and of the

heights. Figure

4 shows

CJ/~~

of the torus and the

sphere.

A

change

to L~ behaviour is very

unlikely

and for that

reason the data

strongly

suggest a continuous

phase

transition in

agreement

with

previous

work [8, 14-17,

38, 39].

From the data shown in

figure

4 we can obtain the

following

upper

boundaries of critical exponents

Sphere: ~

s 0.00 + 0.04 Torus:

~

s 0.06 + 0.02

(11)

(7)

Using

this

simple method,

we cannot

distinguish

a

diverging specific

heat with very small but

positiv

a, a

logarithmic divergence

a, = 0 and a power law cusp a, <

0,

where a, denotes the exponent of the

singular

part of the

specific

heat. We will use the abbreviation a instead of a,.

Following

Fisher [40], these three cases may be

distinguished

with a fit of the form

C(Al)

= A

(Al~~ I)

+ B

,

Al =

[lf 1[ (12)

Figure

5 shows such fits for a

= 0.I

(power law),

a = -0.01

(near logarithmic)

and a

=

-1.2,

-2.0

(power

law

cusp).

The fits

clearly

favour a power law cusp of the

specific

heat with

a

large negative

value of a,

although

we were not able to estimate the exponent a

precisely.

6 6

5.5 36 - 5.5 36 - .--=1

~ 64 - 64 4"I

~ IDS -

~ lot

-

4.5 144 - 4.5 144 - _,

~ 28K -

~ 28K -

432 - 432

3 5 3 5

3 "

3

2.5 2.5

~ ~

l.5 1.5

l i

o.5 o.5

lo 5 o 5 lo lo 5 o 5 lo

x x

6 6

5.5 36 - 5.5 36

64 64

log -

5 lo~ -

4.5 144 - 4.5 144 -

~ 288 - 28K -

432 - 4 432 -

3.5 3.5

3 " 3

25 2.5

2 2

1.5 l.5

l j

o.5 05

08 -0.6 -DA -0.2 0 0.2 0A 0.6 0.8 0.6 DA 02 0 o.2 DA 0.6

x x

Fig-S-

Plot of the specific heat c against z

=

(al~° -1)

with a

= 0.1

(upper left),

-0.01

(upper right),

-1.2

(lower left)

and a a

= -2.0

(lower right).

Our results are in contrast to the estimates of Renken and

Kogut

[39]

a/vd

=

0.14(3)

for the

sphere. They

assumed

scaling

above N = 72, but the more accurate data in

Figure

4 shows that this

assumption

is not true. The

decreasing slope

in

Figure

4 is also present in their

Figure

5 [39]

although

this is

slightly

masked

by larger

error barrs and less data

points.

Catteral et all. [38]

reported

an estimate of

a/vd

=

0.185(50),

but

they

used a different discretization based

on

#~ graphs

with a

flip

acceptance rate of

only O(I$l)

at

lc

cS I-S and

larger

correlation times of the

edge

extrinsic curvature than in our discretization.

(8)

Another

possibility

to determine the order of the transition is the cumulant VN of the

edge

extrinsic curvature

VN := 1-

~~~~ )

,

(13) ie~)~g

which behaves

quite differently

at temperature driven first- and second-order transitions

[33,

34]:

1, and 2.order: VN)ruin

'~I" T#Tcfixed (14)

2,order: VN)ruin

'~1"

~

T =

Tc(N) (15)

1-order: VN)mjn

'~I"

~

~~~

~

~~ f

T

=

Tc(N) (16)

3(E(

+

Et

E+

and E- are the

energies

of the system above and below the transition. For a very weak first-order transition

(E+

cS

E-)

we also have VN)~n;n *

2/3.

We

computed

VN defined

by equation (13) using again

the method of

Ferrenberg

and Swend-

sen

[36, 37].

The

resulting figures

show the

predicted single peak

minima with

wings following equation (14).

The finite size

dependence

of the minima of VN)~n;n shown in

Figure

6

distinctly

favours the

asymptotic

behaviour in

equation (15)

and therefore a continuous

phase

transition

or a very weak first order transition.

0.67

0.65

0.64 a

)

~

~

0.63

-.

~ ~

0.62 0.61 0.6

0.59

0 0.005 0.01 0.015 0.02 0.025 0.03

IN

Fig.6.

Finite size dependence of the minimum VN )nfin of the reduced cumulant of the edge extrinsic curvature.

(o)

denotes data of the sphere,

(D)

those of the torus and the arrow the large N limit

2/3

of a continuous transition.

In

general,

finite size

scaling predicts

also a shift Al

=

If -16f'

of the effective transition

'temperature' If proportional

to

N~~(= L~~)

for a first- and

proportional

to

N~Q"~(=

L~Q")

for a second-order transition.

Unfortunatly I~°

of

dynanfically triangulated

random surfaces is not known. For that reason, we have to use a twc-parameter fit with unknowns

IT

and vd. But we can

improve

the

reliability

of this

fit,

because we know more.

First,

the fit

(9)

has to be a

straight

line

(neglecting

corrections to

scaling)

and we have

limN-cc Al(N)

= 0.

Second,

the shift

Al(N)

is different for the

specific

heat and the cumulant in

general.

Therefore the

slope

of the fitted lines will be different in

general,

but we stiff have

fimN-co Al(N)

= 0 for both observables.

0.25 0.16

0.14 C -

V -

02 C -

V +- 012

O-1 0.15

~~g

~ o-t

~

l'~

~~~

0 .j

i

o ~o.02

0 o.05 o 0.15 o.2 o.25 o.3 o o.05 0. t o.15 o.2

x x

Fig.?.

Best fit of y = Al against z = N~~'"~ for the sphere

(left part)

and the torus

(right part).

(o)

denotes the specific heat c data,

(D)

those of the cumulant V.

Figure

7 shows the best fits for the

sphere

and the torus. The estimates of the parameters

are

lm

= 1.51 + 0.04

,

ud = 3.2 + 0.5

(17)

for the

sphere

and

lm

= 1.47 + 0.02

,

vd = 2.5 + 0.5

(18)

for the torus.

We turn now to the order parameter itself. Common

practise

is to take

(

=

R/L (R

is the

typical radius,

L the linear size of the

membrane)

to be a suitable order parameter

[41-47].

Initially

[47] it was also defined

as

Rg(L)

=

(L (L

-

oJ),

with the linear size L of the

hexagon

and the radius of

gyration R(c~ £;; IX; X; [~).

A suitable choice for the order parameter therefore is

(

:= R~

IN (19)

with

N

~l~

"

j~r(j~r

i) £'i'i l'~i -'~I)~ (~°)

;,j

a; denotes the number of nearest

neighbours,

I-e- the number of links connected to a node I.

The associated

susceptibility

is

xR» := L~

(1(~) l()~)

=

(

(lR~) lR~)~) (21)

Figure

8 shows the order

parameter (

and

Figure

9 the

susceptibilty

of the

sphere.

The results for the torus are similar.

(10)

0.1

~

0.09

~

wP °

~

0.08 o° ~$ i

0.07

~~

°

j~~ ((

.~~

~ +

~

~

~~

0.04

o

~

° x

432

*

0.03

~

~

~

0.02

~

~ ~

0.01

0

0 0.5 1.5

2

2.5

3

I

Fig.8.

Order parameter (

=

R~

IN

of the sphere. Errors are smaller than symbol size.

0.08

DTRS, sphere

~

0.07

~~

0.06

~

~((

~

0.05

"~

(~

~*~

0.04

~

°.°3

.j~~J

«

,

o o~

_.jj,

'

'».--q~j",,

~

#a..,_"

__

'~~

.-

-«~'

"".)

i

0

0.7

0.8

0.9

1-I

1.21.3 1.41.5 1.6

1.7

1.8

1.9 2 2.I

I

Fig-g-

Susceptibiity XR» of the sphere

(Lines

to guide the

eye).

(11)

5 4.5

4 _,:.." ~:

3.5

~:.."'

3 torus -- _:.""

2 5

sphere

-- __:.""

~..."'

A 2

~

_.-..'"

ii'

_,:."

~~ 1.5 _:.."

V ,.~..'"

l __:.""

,:a."'

0.5

50 100 150

200

300

400500

N

Fig,10.

Scaling of the radius of gyration squared

(R~(N))

at the position of the maximum of the specific heat c~~~

(o)

denots the data of the torus,

(D)

data of the sphere.

0.06

0.05 _,..4""

torus -- __:."

~

0.04 sphere

--

_:.""'

0.03 __:.-."~

_,:...'~

0.02

~,:.""

%,....""

o.oi

50 100 150 200 300

400

N

Fig,ll.

Scaring of the susceptibility X

(Eq. (21), Fig.

9) in the case of a torus

(o)

and a sphere

(°).

(12)

We also measured another

possible

order paramter

I'

=

(R'~) IN,

IN

(R'~)

=

£ (X; X)~

~

i

which exhibits a small increase near the

phase

transition and a slower

decay

of

I'

for 1-0.

The difference is caused

by

a

change

of the internal geometry near the

phase

transition

[32].

With the data for the

sphere

in

figure

8 and the

corresponding

data of the torus one can estimate the critical exponent

fl/vd

of the order parameter

assuming

a second order transition.

Here we use as the effective critical temperature the

position

of the

peak

of the

specific

heat.

C~~~

(cf. Fig. 10).

An estimate of

fl/vd using

results in

Torus:

fl/vd

= 0.28 + 0.02

,

Sphere: fl/vd

= 0.35 + 0.04

(23)

and with the values of vd in

equation (17)

and

(18)

Torus:

fl

= 0.7 + 0.2

,

Sphere: fl

= I.1 + 0.2

(24)

Figure

11 shows the

scaling

of the maxima of the

susceptiblity

X

(Eq. (21), Fig. 9).

The results are

Torus:

7/vd

= 0.62 + 0.06

,

Sphere: 7/vd

= 0.66 + 0.06

(25)

and, using

the values of vd in

equations (17)

and

(18),

Torus: 7 = 1.6 + 0.5

,

Sphere:

7 = 2.1 + 0.5

(26)

With these

large

error bars and estimated values a t3 -1.5 the results are almost

compatible

with the

scaling

relation

a+2fl+7=2 (27)

Acknowiedgements

Partial support

by

the SFB 123 and the BMFT

project

0326657D and 031240284 is

gratefully acknowledged.

References

[ii

Polyakov A., Phys. Lett. 103B

(1981)

207.

[2] Fendler J, and Tundo P., Acc. Chem. Res. 17

(1984)

3.

[3] Larche F., Ape]] J., Bassereau P, and Marignan J., Phys. Rev. Lett. 56

(1986)

1700.

[4] Kantor Y, and Nelson, D., Phys. Rev. Lett. 58

(1987)

2774.

[5] Ambj#m J,, Durhuus B. and Fr6hlich J,, Nucl, Phys, 8257

(1985)

433.

[6] David F., Nucl. Phys. 8257

(1985)

543.

(13)

[7] Boulatov D., Kazakov V., Kostov I. and Migdal A., Nucl. Phys. 8275

(1986)

641.

[8] Renken R. and

Kogut

R., Nud. Phys.

8354(1991)

328.

[9] Renken R, and

Kogut

J., Nud. Phys. 8350

(1991)

554.

[10] Renken R, and

Kogut

J., Nucl. Phys. 8342

(1990)

753.

[ii]

Onogi T., Phys. Lett.

8255(1991)

209.

[12] Harnish R, and Wheater J., Nud. Phys.

8350(1991)

861.

[13] Baig M., Espriu D. and Wheater J., Nud. Pl~ys.

B314(1989)

587.

[14] Baillie C., Williams R., Catteral S, and Johnston D., Nucl. Phys.

8348(1991)

543.

[15] Baillie C., Johnston D. and Wiliams R., Nud. Phys.

8335(1990)

469.

[16] Catteral S., Phys. Lett.

8243(1990)

121.

[17] Catteral S., Phys. Lett. 8220

(1989)

207.

[18]

Ambjarn J., Durhuus B, and Jonsson T., Nucl. Phys.

8316(1989)

526.

[19] Peliti L. and Leibler S., Phys. Rev. Lett.

54(1985)

1690.

[20] Helfrich W., J. Phys.

46(1985)

1263.

[21] F6rster D., Phys. Lett. France114A

(1986)

lls.

[22] Polyakov A., Nud. Phys. 2688

(1986)

406.

[23] Ambj#m J, and Durhuus B., Phys. Left.

8188(1987)

253.

[24] Ambj#m J., Durhuus B. and Jonsson T., Phys. Rev. Lett.

58(1987)

2619.

[25] Ambj#m J., Durhuus B., Fr6hlich J. and Jonsson T., Nud. Phys.

8290(1987)

480.

[26] Espriu D., Phys. Lett.

1948(1987)

271.

[27] Rouse P., J. Chem. Phys.

21(1953)

1272.

[28] Doi M. and Edwards S., The Theory of Polymer Dynamics,

(Clarendon

Press, Oxford,

1986).

[29] Kalos M. and Whitlock P., Monte Carlo Methods, Vol. 1

(Wiley,

New York,

1986).

[30] Heermann D., Computer Simulation Methods in Theoretical Physics, 2nd ed.

(Springer

Verlag, Heidelberg,

1990).

[31] Binder K. and Heermann D., Monte Carlo Simulation in Statistical Physics, Second edition

(Springer-Verlag

Heidelberg,

1992).

[32] Mfinkel C. and Heermann D., J. Phys.

12(1992)

2181.

[33] Challa M., Landau D, and Binder K., J. Phys. II

France1(1986)

37.

[34] Binder K. and Landau D., Phys. Rev.

308(1984)

1477.

[35] Peczak P. and Landau D., Phys, Rev.

398(1988)

11932.

[36] Ferrenberg A. and Swendsen R., Phys. Rev. Lett.

63(1989)

1195.

[37]

Ferrenberg

A. and Swendsen R., Phys. Rev. Lett.

61(1988)

2635.

[38] Catteral S., Eisenstein D., Kogut J. and Renken R., Nucl. Phys.

8366(1991)

647.

[39] Renken R. and Kogut R., Nud. Phys. 8348

(1991)

580.

[40] Fisher M., The theory of critical point singularities, in Proceedings of the International School of Physics 'Enrico Fermi'

(1971).

[41] Abraham F, and Kardar M., Sdence 252

(1991)

419.

[42] Abraham F, and Nelson D., J. Phys. France

51(1990)

2653.

[43] Abraham F. and Nelson D., Science

249(1990)

393.

[44] Bouchaud J, and Bouchaud E., Phys. Rev. Lett.

61(1988)

2625.

[45] Guitter E., David F., Leibler S. and Peliti L., Phys. Rev. Lett.

61(1988)

2949.

[46] Paczuski M., Kardar M. and Nelson D., Phys. Rev. Lett.

60(1988)

2638.

[47] Kantor Y, and Nelson D., Phys. Rev.

A36(1987)

4020.

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