Ab initio molecular dynamics (MD)

Ab initio molecular dynamics (MD)
1985 Car and Parrinello apply ab initio methods, based
on density functional theory (DFT), to MD:
Electronic structure of complex chemical systems
Optimized geometry (minimum energy)
System evolution
Simulations length ≈ ps (classical MD ns)
Surface induced crystal structures

Interactions between organic molecules and solid
substrate have relevant effects for molecular electronics
The theoretical approach is difficult because of the
considerable complexity of the problem
Surface induced crystal structures

Chemisorption of thiophene on Si(001)
Costanzo, Venuti, Silvestrelli, Della Valle and Brillante (2009)
Surface induced crystal structures

Not only chemisorption but also physisorption will be
considered
A novel approach from Silvestrelli will be used:
P. Silvestrelli, Phys Rev Lett. (2008), 100 pag. 053002
Surface induced crystal structures

Chemisorption of sexithiophene on Si(001)
Surface induced crystal structures

Work function for T4 on Si(001)
ΔVel= 10.5 eV
Energy (eV)
ΔVel= 10.8 eV
ΔVel= 10.5 eV
Z (Å)
Z (Å)
Preliminary calculations suggest that the work function is
affected by chemisorption of oligothiophene on the Si surface
[Resel et al, J. Appl. Phys. (2004) 96, pag. 2716].
Surface induced crystal structures

Observables:
Electronic properties of the system: atomic charges, spin
density, electronic spin density, dipole surface etc
Vibrational and optical properties: frequencies of normal
modes of vibration, optical conductivity, polarizability
(Raman spectra), hyperfine couplings of EPR spectra
Structural properties of molecules: ions,
complexes
radicals,
Kinetics and thermodynamic properties: stability of the
compounds, activation barriers and reaction velocity
Surface induced crystal structures