Method & Basis Explainer
Student-friendly cards for common methods, basis sets, and job types.
Functional
B3LYP
Best for: General organic molecules, geometry optimization
Watch out: Misses dispersion without D3; slow for large systems
Typical use: Opt + Freq, small/medium organics
Recommended pairing: B3LYP-D3 + def2-TZVP
Functional
PBE0
Best for: Balanced accuracy, transition metals
Watch out: May underbind noncovalent systems
Typical use: Single points on optimized geometries
Recommended pairing: PBE0-D3 + def2-TZVP
Functional
wB97X-D
Best for: Noncovalent interactions, TS screening
Watch out: Heavier for large systems
Typical use: Dispersion-sensitive studies
Recommended pairing: wB97X-D + def2-TZVP
Functional
M06-2X
Best for: Main-group thermochemistry, kinetics
Watch out: Sometimes inconsistent for metals
Typical use: Energetics, barriers
Recommended pairing: M06-2X + def2-TZVP
Basis
6-31G(d)
Best for: Quick optimizations
Watch out: Limited for anions and dispersion
Typical use: Initial structure relaxation
Recommended pairing: B3LYP + 6-31G(d)
Basis
6-31+G(d,p)
Best for: Anions, lone pairs
Watch out: Still modest for high accuracy
Typical use: Charge-sensitive SP calculations
Recommended pairing: B3LYP-D3 + 6-31+G(d,p)
Basis
def2-SVP
Best for: Fast screening
Watch out: Not ideal for final energies
Typical use: Initial geometry scans
Recommended pairing: PBE0 + def2-SVP
Basis
def2-TZVP
Best for: Production-quality results
Watch out: Higher cost
Typical use: Final single points
Recommended pairing: wB97X-D + def2-TZVP
Job Type
Opt
Best for: Finding equilibrium geometry
Watch out: May converge to local minima
Typical use: Structural optimization
Recommended pairing: Opt + Freq
Job Type
Freq
Best for: Vibrational analysis
Watch out: Sensitive to basis choice
Typical use: Confirm minima / TS
Recommended pairing: Opt + Freq
Job Type
SP
Best for: Single point energies
Watch out: No geometry change
Typical use: Energy refinement
Recommended pairing: SP on optimized geometry