.. highlight:: none

.. _Subsec:pairlift:

PairLift file
~~~~~~~~~~~~~~~~~~~~

This file determines the coefficients of the pair-lift couplings given by

.. math::
   \mathcal{H} = \sum_{i,j} J_{ij}^{\rm PairLift}
   (c_ {i\uparrow}^{\dagger} c_{i\downarrow}^{\phantom{\dagger}} c_{j\uparrow}^{\dagger} c_{j\downarrow}^{\phantom{\dagger}}
   + c_ {i\downarrow}^{\dagger} c_{i\uparrow}^{\phantom{\dagger}} c_{j\downarrow}^{\dagger} c_{j\uparrow}^{\phantom{\dagger}}) .

An example of the file format is presented below.

::

    ====================== 
    NPairLift 6  
    ====================== 
    ========NPairLift ====== 
    ====================== 
       0     1  0.50000
       1     2  0.50000
       2     3  0.50000
       3     4  0.50000
       4     5  0.50000
       5     0  0.50000

File format
^^^^^^^^^^^

-  Line 1: Header

-  Line 2: ``[npairlift] [count]``

-  Lines 3-5: Header

-  Lines 6-: ``[i] [j] [val]``

Parameters
^^^^^^^^^^

-  ``[npairlift]``

   **Type :**
   String (blank is not allowed)

   **Description :**
   An arbitrary keyword for the total number of the pair-lift couplings.

-  ``[count]``

   **Type :**
   Integer (blank is not allowed)

   **Description :**
   An integer giving the total number of the pair-lift couplings.

-  ``[i]``, ``[j]``

   **Type :**
   Integer (blank is not allowed)

   **Description :**
   An integer giving a site index (:math:`0 \le i, j < {\rm Nsite}`).

-  ``[val]``

   **Type :**
   Double (blank is not allowed)

   **Description :**
   A value for :math:`J_{ij}^{\rm PairLift}`.

Usage rules
^^^^^^^^^^^

-  Headers cannot be omitted.

-  The program is terminated with error if there are duplicated entries.

-  The program is terminated with error when the number of entries is different from ``[count]``.

-  The program is terminated with error if
   ``[i]`` or ``[j]``
   are outside the range of the defined values.


.. raw:: latex

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