Dear Mohammad,

The energy you've got looks pretty good to me. In that paper they report -0.7569, and you probably studied larger system sizes.(maybe?) Anyway, you may know already that the ferrimagnetic system you are studying has a degenrate ground state: it's a multiplet with total spin Stot=L(S1-S2), where S=1 and S2=1/2 in this case, as clearly explained in this paper. This explains why you've got essentially the same energies. To get the gap you need to calculate E(Stot+1), or set Sz_tot=L(S1-S2)+1

I hope this helps (and works...) Saludos, <ADRIAN>

zhian asadzadeh wrote:

Hi Dear,

I tried to calculate energy gap for ferrimagnetic ladder. in this paper ( Phy Rev B, 63, 054432) it has been done which you can find in table I. I used the periodic boundary condition because in the case of open boundary condition the energy converges very slowly. I have achieved the following result. E0= -0.757036 E1= -0.757032

I have used the following input file: I have tried for inter chain coupling J' = 0.2 with the notation of this paper.

LATTICE="ferrimagnetic ladder" SWEEPS=4 MAXSTATES=300 MODEL="spin", L=30 local_S0=1/2,local_S1=1,Jxy0=1,h=0.0,Jxy1=0.2,Jz1=0.2 BC1=periodic,BC2=periodic NUMBER_EIGENVALUES=2 Jz0=1 {Gamma=0.0;}

which L is the number of unit cell and h, Gamma are longitudinal and transverse magnetic field respectively. Jz0 , Jxy0 are chain couplings and Jz1, and Jxy1 are inter chain couplings. we see that the result is not concur with this paper for energy gap. I see in this paper lanczos method is used but I expect that the result be same in 4 digit. please let me know what is wrong?

Thanks, Mohammad.

On Wed, Mar 18, 2009 at 2:30 PM, <comp-phys-alps-users-request@phys.ethz.ch mailto:comp-phys-alps-users-request@phys.ethz.ch> wrote:

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Today's Topics:

  1. Energy Gap (zhian asadzadeh)
  2. Re: Energy Gap (Matthias Troyer)


----------------------------------------------------------------------

Message: 1
Date: Tue, 17 Mar 2009 14:43:46 +0330
From: zhian asadzadeh <zhian.asadzadeh@gmail.com
<mailto:zhian.asadzadeh@gmail.com>>
Subject: [ALPS-users] Energy Gap
To: comp-phys-alps-users@phys.ethz.ch
<mailto:comp-phys-alps-users@phys.ethz.ch>
Message-ID:

 <89e5d6760903170413w7e72ef85i873b8d47564f4320@mail.gmail.com
<mailto:89e5d6760903170413w7e72ef85i873b8d47564f4320@mail.gmail.com>>
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Hi Dear,

Thank you for your consideration.
My model is anisotropic Ferrimagnetic chain in transverse magnetic
field.
when I say the result is wrong I mean when I have tried to obtain
energy gap
for some problems and models which have been solved earlier I saw  the
result doesn't agree with those earlier results. for example spin
one and
half-one chain and ferrimagnetic chain and  anisotropic ferrimagnetic
ladder.
Something is not very obvius for me, how DMRG calculate ground
state and
first exited state from one wave function ?!

Thanks,
Zhian.


On Tue, Mar 17, 2009 at 2:30 PM,
<comp-phys-alps-users-request@phys.ethz.ch
<mailto:comp-phys-alps-users-request@phys.ethz.ch>>wrote:

> Send Comp-phys-alps-users mailing list submissions to
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----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 16 Mar 2009 12:33:11 -0700
> From: Matthias Troyer <troyer@phys.ethz.ch
<mailto:troyer@phys.ethz.ch>>
> Subject: Re: [ALPS-users] Energy Gap
> To: comp-phys-alps-users@phys.ethz.ch
<mailto:comp-phys-alps-users@phys.ethz.ch>
> Message-ID: <43E825E5-7BE3-4EA0-9C2A-20A1FC8C21AF@phys.ethz.ch
<mailto:43E825E5-7BE3-4EA0-9C2A-20A1FC8C21AF@phys.ethz.ch>>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
>
> On Mar 16, 2009, at 2:01 AM, zhian asadzadeh wrote:
>
> > Hi All,
> >
> > I want to calculate energy gap for spin chain with DMRG. I set
> > NUM_EIGENVALUES=2 in my parm file but the result which
 achieved is
> > wrong.
> > Is it necessary to determine something else for example the sector
> > which DMRG work in it? in my problem I dont have any good symmetry
> > and I can not easily determine the sector which the first exited
> > state is in it. I would be very appreciate if someone could please
> > help me.
> >
> > Thanks,
> > Zhian.
>
> Can you please send more details about your model, or better yet the
> input file? An what do you mean exactly by saying that the result is
> wrong?
>
> Matthias
>
>
>
> End of Comp-phys-alps-users Digest, Vol 36, Issue 10
> ****************************************************
>