Hi Joseph,

You will modify the source file tebd.f90, which also means you will need to re-build ALPS from source when you are finished.  The lines to modify are 162-176, in which the array "carray" is constructed.  This array specifies a product state \prod_{i=1}^L \sum_{j=1}^d c_{i j} |i_j>, where d is the local dimension of a single site, L is the number of lattice sites, and c_{i j} is the expansion of the wavefunction at site i in the local basis states |i_j>.  The coefficients c_{i j} are stored as carray(j,i).  You will also want to set qSwitch to .false. if your initial eigenstate is not an eigenstate of S_z.  Hope this helps.

-Michael


On Wed, Aug 7, 2013 at 5:26 AM, Joseph Prentice <Joseph.Prentice@physics.ox.ac.uk> wrote:
Hi Michael,

I see, I thought that might be the case. I know very little about Fortran, but if it's possible to set up this initial Hamiltonian/state, I'd like to give it a go, even if I am unable to get it to work. Could I have further details on this please?

Thank you,
Joseph

On 7 Aug 2013, at 11:00, <comp-phys-alps-users-request@lists.phys.ethz.ch>
 wrote:

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>   1. Question concerning an initial state in TEBD (Joseph Prentice)
>   2. Re: Question concerning an initial state in TEBD (Michael Wall)
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> Message: 1
> Date: Tue, 6 Aug 2013 12:25:40 +0000
> From: Joseph Prentice <Joseph.Prentice@physics.ox.ac.uk>
> To: "<comp-phys-alps-users@lists.phys.ethz.ch>"
>       <comp-phys-alps-users@lists.phys.ethz.ch>
> Subject: [ALPS-users] Question concerning an initial state in TEBD
> Message-ID:
>       <747861816F6A5C47BE50FCA07F5B2B4A0DF3D2@EXCHNG16.physics.ox.ac.uk>
> Content-Type: text/plain; charset="us-ascii"
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> Hi again all,
>
> I just had a short question about the TEBD code in ALPS. I would like to study the evolution of an initial state that is a Neel state, but rotated by an angle /alpha about the y-axis, under the XXZ Hamiltonian. A Hamiltonian whose ground state would be the right one would simply have a magnetic field along the direction of /alpha that swaps direction at each site i.e. (-1)^l *(cos /alpha *S^z_l + sin /alpha *S^x_l) where l is the site number, but I can't see a way to put this into the code. Is alternating the sign of the interaction in this way possible?
> Also, if there is another way of producing such a state in the TEBD code, it would be wonderful if someone pointed it out, I would be very grateful.
>
> Thank you very much,
>
> Joseph Prentice
>
> ------------------------------
>
> Message: 2
> Date: Tue, 6 Aug 2013 14:31:20 -0600
> From: Michael Wall <mwall.physics@gmail.com>
> To: comp-phys-alps-users@lists.phys.ethz.ch
> Subject: Re: [ALPS-users] Question concerning an initial state in TEBD
> Message-ID:
>       <CA+DwVMoeLK_TfLEi4DGHCkG7riYn3MHOZz6=E3TaPLcxcekBLQ@mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi Joseph,
>
> At present, the only initial states supported by tebd are ground states of
> translation-invariant Hamiltonians or the 'kink' initial state used in the
> spin tutorials.  You can edit the source file tebd.f90 to write in another
> product state of your choice.  If this is the route you would like to
> follow I can give you more details.  The next generation of MPS codes for
> ALPS will include much greater flexibility in the choice of initial state.
>
> -Michael
>
>
> On Tue, Aug 6, 2013 at 6:25 AM, Joseph Prentice <
> Joseph.Prentice@physics.ox.ac.uk> wrote:
>
>> Hi again all,
>>
>> I just had a short question about the TEBD code in ALPS. I would like to
>> study the evolution of an initial state that is a Neel state, but rotated
>> by an angle /alpha about the y-axis, under the XXZ Hamiltonian. A
>> Hamiltonian whose ground state would be the right one would simply have a
>> magnetic field along the direction of /alpha that swaps direction at each
>> site i.e. (-1)^l *(cos /alpha *S^z_l + sin /alpha *S^x_l) where l is the
>> site number, but I can't see a way to put this into the code. Is
>> alternating the sign of the interaction in this way possible?
>> Also, if there is another way of producing such a state in the TEBD code,
>> it would be wonderful if someone pointed it out, I would be very grateful.
>>
>> Thank you very much,
>>
>> Joseph Prentice
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