Hi,
I have some specific questions regarding the interpretation of DOS plots from DFT softwares (e.g. VASP).
1. What does it mean when the peaks broadened after material alterations (e.g. addition of adsorbate)?
2. What does it mean when the peaks become lower in height after material alteration?
3. What does it mean if the peaks shifted energy (e.g. from being 0.1eV below Fermi Energy to 0.9 eV below Fermi Energy) after material alteration?
4. What is the significance if the peak is near or far from the Fermi energy?
5. What is the significance if the Dirac point and Fermi Energy is coinciding?
6. Can we know from the DOS graphs itself if the binding is covalent or ionic?
7, Can we identify from the DOS graphs if a certain PDOS (e.g. s-orbital) is attributed to bonding or antibonding states?
Thank you very much. I have some ideas from reading papers but I am not sure if they are right so I like to ask here.
the broadening of peaks can be attributed to hybridisation . when the orbitals of the adsorbate and the layer hybridised. Shifting of peak corresponds to changing behaviour of the substance . If dirac point anf fermi enery are corresponding it shows it is a semi metal like graphene. Peak near to fermi level correspond to HOMO or LUMO used to calculate band gap.
Here are some of my ideas, I am not sure if they are correct though.
1. Broadening of peaks corresponds to covalent bonding between the adsorbate and substrate.
6. If there is hybridization and significant peak changes (such as broadening) it is most probably covalent. If there are no significant peak changes, and an orbital from expected donor is above Fermi Energy, this corresponds to the orbital losing electrons and hence the bonding is ionic.
the broadening of peaks can be attributed to hybridisation . when the orbitals of the adsorbate and the layer hybridised. Shifting of peak corresponds to changing behaviour of the substance . If dirac point anf fermi enery are corresponding it shows it is a semi metal like graphene. Peak near to fermi level correspond to HOMO or LUMO used to calculate band gap.
Kindly see the book of Papaconstantpoulos. On Band structures.
Take the case of a simple metal , say Al , you see the free electron parabola.
DOS is some thing like the Sommerfelds free electron parabola.
Check the Integrated DOS. It will be three as there are 3 valence electrons in Al.
So, s electron systems will show free electron behaviour.
d electrons lead to narrow bands.It will be reflected in DOS by peaks. DOS of say Cu will show ups and downs.
It is important to note that the location of the Fermi level If the DOS plot shows a valley (pseudogap-PG ) and if the Fermi level lies on the PG , then it refers to a system having high melting point . On the Other hand if it lies on the right where the DOS is high , it refers to a superconductor .
Bulk glassy systems etc..and shifting the Fermi level and the changes in the Properties are discussed in our papers published in Phys.Rev ( P.Ravindran and R.Asokamani in 1994, -96) .
Best wishes
R.Asokamani ([email protected])
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