VASP Single Point Calculation

Compute the total energy (and optionally charge density, wavefunction) at a fixed geometry. No ionic relaxation.

When to Use

1. After geometry optimization — get a precise energy at the relaxed geometry with tighter settings
2. Before DOS calculation — generate CHGCAR with fine k-mesh for subsequent non-SCF DOS
3. Before band structure — generate CHGCAR for non-SCF band calculation
4. Convergence testing — test ENCUT, k-points, or other parameters at fixed geometry
5. Energy evaluation — compare energies of different configurations without relaxing

Discussion Checkpoints

🔴 Must discuss with user:

• Functional consistency — must match the functional used in the preceding geo_opt; mixing PBE geometry with SCAN single point introduces systematic errors

🟡 Recommend confirming:

• LORBIT (default: 11) — needed for projected DOS; set to 11 for per-atom orbital projections, omit if only total energy is needed
• NEDOS (default: 3001) — increase for DOS analysis to resolve fine features; 301 is sufficient for energy-only calculations
• ISMEAR — use -5 (tetrahedron) for DOS calculations, 0 (Gaussian) for general single points, 1 (Methfessel-Paxton) for metals
• LCHARG / LWAVE — set True if this single point feeds into a subsequent DOS or band structure calculation

🟢 Safe defaults:

• NSW = 0 (no ionic relaxation)
• IBRION = -1 (no ionic optimizer)
• EDIFF = 1E-5
• ISMEAR = 0, SIGMA = 0.05

Basic Single Point

from catgo.workflow import Workflow
from catgo.workflow.builtins import geo_opt, single_point

wf = Workflow("Single point energy")
struct = wf.add_task("structure_input", structure=structure_json)
sp = wf.add_task(single_point, structure=struct.output.structure,
                 system_name="TiO2_SP")
wf.submit()

MCP equivalent:

catgo_workflow_engine(action="create", params={"name": "Single point"})

catgo_workflow_engine(action="add_task", params={
  "workflow_id": "wf_xxx",
  "task_type": "single_point",
  "software": "vasp",
  "structure": "<json>",
  "system_name": "TiO2_SP"
})

catgo_workflow_engine(action="submit", params={"workflow_id": "wf_xxx"})

After Optimization

Chain a single point after relaxation for a more accurate energy:

opt = wf.add_task(geo_opt, structure=struct.output.structure,
                  ISIF=2, system_name="relax")
sp = wf.add_task(single_point, structure=opt.output.structure,
                 ENCUT=600,     # Higher cutoff for precise energy
                 EDIFF=1e-6,    # Tighter SCF convergence
                 system_name="SP_precise")

Pre-DOS Single Point

Generate a converged charge density with a fine k-mesh for subsequent DOS:

sp = wf.add_task(single_point, structure=opt.output.structure,
                 LCHARG=True,    # Write CHGCAR (needed for DOS)
                 LWAVE=True,     # Write WAVECAR (optional, speeds up DOS)
                 ISMEAR=-5,      # Tetrahedron method (accurate DOS)
                 NEDOS=3001,     # Dense energy grid
                 EDIFF=1e-6,     # Tight convergence
                 system_name="SP_for_DOS")

Pre-Band Structure Single Point

Generate CHGCAR for non-SCF band calculation:

sp = wf.add_task(single_point, structure=opt.output.structure,
                 LCHARG=True,    # Write CHGCAR
                 ICHARG=2,       # Self-consistent (generate charge)
                 system_name="SP_for_bands")

Convergence Testing

Test multiple ENCUT values at a fixed geometry:

wf = Workflow("ENCUT convergence")
struct = wf.add_task("structure_input", structure=structure_json)

for encut in [400, 450, 500, 550, 600]:
    wf.add_task(single_point, structure=struct.output.structure,
                ENCUT=encut, system_name=f"ENCUT={encut}")

wf.submit()

MCP equivalent:

catgo_workflow_engine(action="create", params={"name": "ENCUT convergence"})

catgo_workflow_engine(action="add_task", params={
  "workflow_id": "wf_xxx",
  "task_type": "structure_input",
  "structure": "<json>"
})

# Repeat for each ENCUT value
catgo_workflow_engine(action="add_task", params={
  "workflow_id": "wf_xxx",
  "task_type": "single_point",
  "software": "vasp",
  "structure": "{{t_001.output.structure}}",
  "ENCUT": 400,
  "system_name": "ENCUT=400"
})
# ... repeat for 450, 500, 550, 600

Key Parameters

Parameter	Default	Purpose
NSW	0	No ionic steps (fixed geometry)
IBRION	-1	No ionic optimizer
EDIFF	1e-5	SCF convergence (use 1e-6 for precise energy)
NEDOS	3001	Number of DOS points (increase for DOS calculations)
LCHARG	False	Write CHGCAR (set True for DOS/band pre-calc)
LWAVE	False	Write WAVECAR (set True to restart from wavefunction)
ISMEAR	0	Gaussian smearing (use -5 for DOS with tetrahedron)
LORBIT	11	Write projected DOS (DOSCAR with per-atom projections)

ISMEAR Guidance

System type	ISMEAR	SIGMA	Notes
Insulator/semiconductor	0	0.05	Gaussian smearing (default)
Metal	1	0.2	Methfessel-Paxton
DOS calculation	-5	N/A	Tetrahedron with Blochl corrections
Molecule in box	0	0.01	Small sigma, Gamma-only

Rule: ISMEAR=-5 requires at least 3 k-points per direction. Do not use for Gamma-only calculations.

Output

The single_point task produces:

• output.energy — total DFT energy in eV
• output.structure — the (unchanged) input structure

Troubleshooting

Problem	Fix
SCF not converging	Try ALGO=All, increase NELM=400, or AMIX=0.1
Negative NBANDS warning	Increase NBANDS explicitly
Memory error	Reduce NCORE, or increase node count
Wrong energy for magnetic system	Set ISPIN=2, provide MAGMOM