ORCA Geometry Optimization Skill

When to Use

Use this skill when the user wants to:

• Optimize a molecular geometry with ORCA
• Find the minimum energy structure of a molecule
• Relax a molecular cluster or complex

Do NOT use for periodic systems (use VASP or CP2K instead).

Default Parameters

Parameter	Default	Description
orca_method	B3LYP	DFT functional
orca_basis	def2-SVP	Basis set
charge	0	Total charge
multiplicity	1	Spin multiplicity (2S+1)
orca_extra_keywords	""	Additional ORCA keywords

MCP Tool Examples

Basic optimization

First, confirm the structure is loaded:

catgo_view(action: "get_state")

Create workflow and add optimization task:

catgo_workflow_engine(action: "create", params: {
  name: "Benzene optimization"
})

catgo_workflow_engine(action: "add_task", params: {
  workflow_id: "<wf_id>",
  task_type: "geo_opt",
  params: {
    software: "orca",
    orca_method: "B3LYP",
    orca_basis: "def2-SVP",
    charge: 0,
    multiplicity: 1
  }
})

With dispersion correction (D3BJ)

For systems with non-covalent interactions (dimers, host-guest, protein-ligand):

catgo_workflow_engine(action: "add_task", params: {
  workflow_id: "<wf_id>",
  task_type: "geo_opt",
  params: {
    software: "orca",
    orca_method: "B3LYP",
    orca_basis: "def2-TZVP",
    orca_extra_keywords: "D3BJ",
    charge: 0,
    multiplicity: 1
  }
})

With solvent (CPCM)

For solution-phase chemistry:

catgo_workflow_engine(action: "add_task", params: {
  workflow_id: "<wf_id>",
  task_type: "geo_opt",
  params: {
    software: "orca",
    orca_method: "B3LYP",
    orca_basis: "def2-SVP",
    orca_extra_keywords: "CPCM(Water)",
    charge: 0,
    multiplicity: 1
  }
})

Tight optimization convergence

For publication-quality geometries or pre-frequency calculations:

catgo_workflow_engine(action: "add_task", params: {
  workflow_id: "<wf_id>",
  task_type: "geo_opt",
  params: {
    software: "orca",
    orca_method: "B3LYP",
    orca_basis: "def2-TZVP",
    orca_extra_keywords: "TightOpt D3BJ",
    charge: 0,
    multiplicity: 1
  }
})

Open-shell system (radical)

For a doublet radical like NO2:

catgo_workflow_engine(action: "add_task", params: {
  workflow_id: "<wf_id>",
  task_type: "geo_opt",
  params: {
    software: "orca",
    orca_method: "UB3LYP",
    orca_basis: "def2-SVP",
    charge: 0,
    multiplicity: 2
  }
})

Submit the workflow

catgo_workflow_engine(action: "submit", params: {
  workflow_id: "<wf_id>"
})

Check status

catgo_workflow_engine(action: "status", params: {
  workflow_id: "<wf_id>"
})

Get results

catgo_workflow_engine(action: "get_result", params: {
  workflow_id: "<wf_id>",
  task_id: "<task_id>"
})

Dispersion Corrections

Keyword	Method	When to use
D3BJ	Grimme D3 with Becke-Johnson damping	Default choice for dispersion
D3	Grimme D3 with zero damping	Legacy, use D3BJ instead
D4	Grimme D4	Newer, slightly better for metals

Always include dispersion for: molecular dimers, adsorption complexes, conformational searches, anything with pi-stacking or H-bonding.

Basis Set Ladder

Basis	Quality	Cost	Use
def2-SVP	Double-zeta	Low	Screening, initial opt
def2-TZVP	Triple-zeta	Medium	Production geometry
def2-TZVPP	Triple-zeta+pol	High	Accurate energetics
def2-QZVPP	Quadruple-zeta	Very high	Benchmark only

Strategy: optimize with def2-SVP, then single-point with def2-TZVP for energy.

SCF Convergence Issues

If ORCA SCF does not converge, try adding to orca_extra_keywords:

• SlowConv -- dampened SCF for difficult cases
• VerySlowConv -- even more conservative
• SOSCF -- second-order SCF (helps for transition metals)
• SmearTemp 5000 -- Fermi smearing for near-degenerate orbitals

Common Mistakes

• Forgetting dispersion for non-covalent systems (huge geometry errors)
• Using restricted (R) method for open-shell (use UB3LYP, not B3LYP)
• Basis set too large for optimization (optimize with SVP, refine energy with TZVP)
• Not checking for imaginary frequencies after optimization