[Pw_forum] adsorption calculations with spin-polarization

[vega lew]

Dear all,

I want to calculate O2 adsorped on certain defect free TiO2 surface. It is
well known that the most stable state for O2 is triplet. Test calculations
showed that the singlet state of O2 was ~*1.13 eV higher* than triplet
state. So we should set nspin = 2, multiplicity = 3, for O2 isolate
molecule. When O2 adsorbed on the defect free TiO2 surface in the slab
model, we still compared the calculations with or without 'nspin = 2,
multiplicity = 3'. The singlet state of the slab model of adsorption is ~*0.82
eV higher *than triplet state. So I think the triplet is suitable for this
adsoprtion slab model. However, the singlet state is the most stable sate
for the bare surface slab model. The triplet stateis of bare surface model
about  ~*1.67 eV higher *than singlet state. So I wonder how to determin the
adsorption energy for this system. E(adsorption)= E(O2+surface)_triplet -
E(surface)_*singlet* - E(isolate O2)_triplet? or E(adsorption)=
E(O2+surface)_triplet - E(surface)_*triplet* - E(isolate O2)_triplet?

I also confused about when spin-polarization is indispensablethe for the
calculation of adsorption behaviours on the surface slab model.

Thank you for reading.

best wishes,

vega

-- 
==================================================================================
Vega Lew ( weijia liu)
Graduate student
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
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Email: vegalew at gmail.com
Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
Jiangsu, China
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