I have quesitons about the computing band and density of the states of the system using Dmol3,

The manual show like this :

When that run is complete, you should make copies of the .car,  .tpvec, .tpdensk and .tpotl files that will be  used in all subsequent properties runs:

cp seedname.car seedname_BandStr.car
cp seedname.car seedname_DOS.car
cp seedname.tpvec seedname_BandStr.tpvec
cp seedname.tpvec seedname_DOS.tpvec
etc
Specifically, one needs the following files for a DOS calculation:

seedname_DOS.tpvec
seedname_DOS.tpotl
seedname_DOS.car
seedname_DOS.kpoints (for periodic structures only)
seedname_DOS.tpdensk (for periodic structures only)
and the following files for a Band structure calculation:

seedname_BandStr.tpvec
seedname_BandStr.tpotl
seedname_BandStr.car
seedname_BandStr.kpoints (for periodic structures only)
seedname_BandStr.tpdensk (for periodic structures only)

When the appropriate copies have been made, execute RunDMol3 for  each properties run:

RunDMol3.sh -nodelete seedname_DOS
RunDMol3.sh -nodelete seedname_BandStr
These jobs can be run independently because they do not share input or output  files.

When compute the band and density of the states of  the periodic structure ,is the tpotl  necessary or not ?
It seem as if the tpotl stores the information of the isolates molecular's information ,based belows :
Restarting with the SCF coefficients
When a molecular DMol3 calculation completes, two files  (.tpvec and  .tpotl) containing the MO coefficients and SCF  eigenvectors are returned and placed in the results folder for the calculation.  (For periodic DMol3 jobs, instead of .tpvec, a  .tpdensk file is used.) The file is hidden, so you  will not see it in the Project Explorer. Using this file to start a subsequent  SCF calculation will reduce the number of iterations needed to reach  convergence.
Note. The .tpvec,  .tpdensk, and .tpotl files are binary,  and can only be used on the platform on which it was created. So, the  .tpvec and .tpotl files can only be used to restart a  run on the same platform.
Whenever the .tpvec (or .tpdensk) and  .tpotl files are present, they will be uploaded to the server, but  they will not be read unless you instruct DMol3 to do so. To submit a  DMol3 job that makes use of these files, perform the following  steps:
It pussles me for a long time !Any suggestions !