Total DOS (TDOS) and Parial DOS (PDOS)

Posted on : February 06, 2021 (Sat) 00:53:17

by kristofer

Dear all

I got peaks in the pdos larger than the peaks of the TDOS, my question is about difference between Total and Partial DOS.

Why does TDOS not match with addition of PDOS?

[Re:03] Total DOS (TDOS) and Parial DOS (PDOS)

Posted on : February 15, 2021 (Mon) 21:40:53

by root

If you use ASA (atomic sphere approximation mode, such as "pheasa" for LDA/GGA specification, the weighted sum of partial DOS coincides with the total DOS in principle.However, it is only "in principle". Actually happening is that they do not coincide with each other. The reason is that the partial DOS and total DOS are calculated in completely different ways. Note that even the energy mesh points calculated DOS are different between partial and total DOS as you can see in the output. Also if the DOS has a peaky structure, the peak values often differ considerably. Of course I such cases, the sum of the partial DOS may exceed the total DOS. (but this is not meaningful). If you do not like such a discrepancy, just calculate dotal DOS from the sum of weighted partial DOS (but be careful: you have to use ASA mode).

[Re:02] Total DOS (TDOS) and Parial DOS (PDOS)

Posted on : February 15, 2021 (Mon) 18:11:24

by kristofer

Dear administrator,
thank you for your response.

... However, if the weighted sum of the partial DOS is taken, where the weight being proportional to the concentration of atoms within the unit cell, does note exceed the total DOS. ...

I have a remark, is it doses note exceed the total DOS or thatis doses not exceed the total DOS.

[Re:01] Total DOS (TDOS) and Parial DOS (PDOS)

Posted on : February 06, 2021 (Sat) 09:46:51

by root

It depends on the situation: if you are calculating cases where a single atom is contained in the unit cell, the sum of partial DOS always slightly smaller than the total DOS. This is because total DOS is calculated from the number of the states below each energy and is the sum of all contribution including higher angular momentum components that is not obtained in the partial DOS (partial DOS's are those of angular momentum smaller than l_max and also only the contributions integrated within a muffin-tin or atomic sphere). If you are calculating disordered alloy systems, including an impurity limit, or systems with more than a single atom per unit cell, the sum of partial DOS in many cases exceeds the total DOS and this is quite correct. However, if the weighted sum of the partial DOS is taken, where the weight being proportional to the concentration of atoms within the unit cell, does note exceed the total DOS. Another case you might meet occurs when you have a very peaky structure. It may happen that the peak hight exceeds that of total DOS. This again because the total DOS is calculated from the number of the states below each energy and the DOS is obtained by differentiating it, showing a kind of smearing.