How we can build a crystalline structure with Molden?

Of course if you already have your molecule in a file format that supports and contains crystal information, just read it in to molden. Molden supports the following file formats with crystal information:

FDAT, CSSR, (BioSYM) CAR, MSF (QUANTA), Mol2 (Sybyl), ShelX, MSI, CONTCAR (VASP)

If you dont have crystal information for your molecule, here is the procedure to create it from scratch:

1 First you build your molecule with the z-matrix builder.
  or you read in your molecule from any of the supported file formats
  
2 Go out of the z-matrix editor and click the cell icon 
  (4th from the top in the "molden control" window click "Packed-Cell 1".
  
3 Then from the cell icon select "Edit Cell Parameters"
  Change the spacegroup and/or a,b,c alpha,beta, gamma
  
  When you change the spacegroup you will have some molecules sticking
  through each other, this wont do. To give all these symmetry copies   
  some more room, increase a,b,c.
  
4 Lets get these molecules apart. Pick from the cell icon:
  "Cell Rot On/Off"
  Now use the arrow buttons in the molden control window to change the
  position of the original molecule in the cell (the symmetry copies will
  also move). To speed things up a little you can click on the "circle"
  icon in between the arrow buttons (this determines stepsize in angle
  rotation and translation). The "in" and "Out" buttons also stand for
  one of the translation dimensions.

  In addition you can rotate the molecules the same way as your used to
  without a cell. One missing degree of rotation can only be reached
  by switching to the "old style" rotation (Click the "Dot" like icon 
  near the arrow buttons) and use the Shift key together with placing
  the pointer in the center of the screen and holding down the mouse
  button. (This is the missing Z-rotation).
  Use Escape in the drawing window to switch off this mode again.


5 save the crystal in one of the supported crystal formats:
  Click the Write button and choose one of the following:

  Mol2,MSF,CSSR,MSI 

  or the write button from the Cell icon dropdown menu: 

  DMAREL, CRYSTAL95, SHELX, VASP, CPMD etc.