methods. The calculations are often carried out for model surfaces (symmetric or
asymmetric slabs) or structural fragments containing catalytically active sites cut
from a larger structure and frozen to preserve the original structure or subjected to
the relaxation procedure. Detailed information on the methods and approximations
commonly used in the context of catalytic properties of materials can be found inter
alia in [140–143].
1.3.2 Model Structure Simplifications and Approximations
(Theory Level)
The simplifications and idealizations discussed above relate to the reduction of the
complexity of the structure and hence a significant reduction in the calculation time.
In most cases, it is a necessary, but insufficient step to be able to effectively simulate
the properties of the material of interest. Another, even more important step, concerns the necessity to make a decision regarding the applied level of theory (type of
approximations), since this will strongly influence the ability to get the results of
acceptable quality in reasonable time, which strongly depends on the particular
choice of the formalism, theory level, and complexity of the system.
In general case, a careful decision should be made regarding:
• The choice of the formalism to be used in calculations—classical (with chosen
appropriate classical Force Field), semi-empirical (with approximate
Hamiltonian, e.g., HMO, PPP, EH, CNDO, INDO, MNDO, AM1, PM3, PM6),
Hartree–Fock, DFT, TD-DFT, etc.;
• Relativistic treatment of the electrons—non-relativistic, semi-relativistic, fully
relativistic;
• Spin treatment—non-spin-polarized or spin-polarized (with particular magnetic
ordering in periodic solids);
• Representation of 3D bulk—non-periodic (cluster) versus periodic (unit cell)
and 2D surfaces—asymmetric slab, symmetric slab, cluster;
• Form of external potential in periodic systems—muffin tin (MT), atomic sphere
approximation (ASA), full potential (FP), or pseudopotential (PP);
• In case of ab initio methods, additionally the choice of electronic interactions
treatment (described earlier) has to be done;
– For HF formalism, the level of post-HF approximation
Configuration Interaction (Full-CI, CIS, CISD, CISDT, MRCI, MRSDCI,
…);
Møller–Plesset Perturbation Theory (MP2, MP3, MP4, …);
Coupled Cluster Theory (CC, CCSD, CCSD(T), …);
Other (QCI, CASSCF, G1, G2, G3 or G4, FPD, ccCA, CBS, …);
40
A. Koleżyński
asymmetric slabs) or structural fragments containing catalytically active sites cut
from a larger structure and frozen to preserve the original structure or subjected to
the relaxation procedure. Detailed information on the methods and approximations
commonly used in the context of catalytic properties of materials can be found inter
alia in [140–143].
1.3.2 Model Structure Simplifications and Approximations
(Theory Level)
The simplifications and idealizations discussed above relate to the reduction of the
complexity of the structure and hence a significant reduction in the calculation time.
In most cases, it is a necessary, but insufficient step to be able to effectively simulate
the properties of the material of interest. Another, even more important step, concerns the necessity to make a decision regarding the applied level of theory (type of
approximations), since this will strongly influence the ability to get the results of
acceptable quality in reasonable time, which strongly depends on the particular
choice of the formalism, theory level, and complexity of the system.
In general case, a careful decision should be made regarding:
• The choice of the formalism to be used in calculations—classical (with chosen
appropriate classical Force Field), semi-empirical (with approximate
Hamiltonian, e.g., HMO, PPP, EH, CNDO, INDO, MNDO, AM1, PM3, PM6),
Hartree–Fock, DFT, TD-DFT, etc.;
• Relativistic treatment of the electrons—non-relativistic, semi-relativistic, fully
relativistic;
• Spin treatment—non-spin-polarized or spin-polarized (with particular magnetic
ordering in periodic solids);
• Representation of 3D bulk—non-periodic (cluster) versus periodic (unit cell)
and 2D surfaces—asymmetric slab, symmetric slab, cluster;
• Form of external potential in periodic systems—muffin tin (MT), atomic sphere
approximation (ASA), full potential (FP), or pseudopotential (PP);
• In case of ab initio methods, additionally the choice of electronic interactions
treatment (described earlier) has to be done;
– For HF formalism, the level of post-HF approximation
Configuration Interaction (Full-CI, CIS, CISD, CISDT, MRCI, MRSDCI,
…);
Møller–Plesset Perturbation Theory (MP2, MP3, MP4, …);
Coupled Cluster Theory (CC, CCSD, CCSD(T), …);
Other (QCI, CASSCF, G1, G2, G3 or G4, FPD, ccCA, CBS, …);
40
A. Koleżyński