--- name: chem-dft-orca-advanced-calculation description: Write and run custom ORCA input files for advanced electronic structure methods or settings not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF, NMR/EPR, and more. category: [chemistry] ---

# Advanced ORCA Calculation

## Goal

Enable advanced ORCA quantum chemistry calculations by constructing a custom ORCA input file from scratch. This skill covers methods and features not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF settings, NMR/EPR properties, and more.

> [!IMPORTANT] > For **standard DFT single-point** calculations (energy, gradients, Hessian), use the [singlepoint skill](../chem-dft-orca-singlepoint/SKILL.md) instead. For **geometry optimization**, use the [optimization skill](../chem-dft-orca-optimization/SKILL.md). This skill is for cases where those wrappers do not expose the needed method or settings.

## 1. Prerequisites

- **Conda environment:** `orca-agent` with `ase` installed (SCINE not required for this skill) - **ORCA binary:** The environment variable `ORCA_BINARY_PATH` must point to the ORCA executable ```bash export ORCA_BINARY_PATH=/path/to/orca ``` - **ORCA documentation:** Consult the [ORCA 6.1 tutorials](https://www.faccts.de/docs/orca/6.1/tutorials/index.html) for method-specific input syntax, keyword blocks, and recommended settings

## 2. Workflow

### Step 1: Understand the user's request

Identify the target method, property, and system. Determine which ORCA keywords and blocks are needed. If unsure, consult the tutorials linked above for the specific method.

### Step 2: Write the ORCA input file

Create a `.inp` file following ORCA input syntax. Every input file should include:

**Mandatory elements:** - A keyword line starting with `!` specifying the method, basis set, and job type - A `*xyzfile` entry referencesing an external .xyz file

**Strongly recommended elements:** - `%pal nprocs N end`: parallelization (always set this to avoid single-core runs) - `%maxcore M`: memory per core in MB (e.g. 4000 for 4 GB per core)

**Example — TD-DFT excited states:** ``` ! B3LYP def2-TZVP TightSCF %pal nprocs 4 end %maxcore 4000

%tddft NRoots 10 MaxDim 5 end

* xyzfile 0 1 molecule.xyz ```

**Example: DLPNO-CCSD(T) single point:** ``` ! DLPNO-CCSD(T) def2-TZVPP def2-TZVPP/C TightSCF %pal nprocs 8 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: Geometry optimization with frequency calculation:** ``` ! B3LYP def2-TZVP D3BJ Opt Freq TightSCF %pal nprocs 4 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: CASSCF multi-reference:** ``` ! CASSCF def2-TZVP %pal nprocs 4 end %maxcore 8000

%casscf nel 6 norb 6 nroots 3 end

* xyzfile 0 1 molecule.xyz ```

> [!TIP] > When using an external `.xyz` file with `* xyzfile charge mult filename.xyz`, the `.xyz` file must be placed in the same directory where ORCA runs (the `--output_dir`).

### Step 3: Run the calculation

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/run_orca_input.py \ --input_file calculation.inp \ --output_dir research/my_project/advanced_calc ```

The script will: 1. Validate basic input structure and warn about missing `%pal`/`%maxcore` 2. Copy the input file to the output directory 3. Execute ORCA and capture all output 4. Parse the final electronic energy from the output 5. Save a `calculation_results.json` summary

### Step 4: Parse results

For standard energies, the runner script already extracts the final energy. For other properties, use the dedicated parser:

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/parse_orca_output.py \ --output_file research/my_project/advanced_calc/calculation.out \ --property energy orbitals ```

Available `--property` options in the parser: - `energy`: Final energy, nuclear repulsion, dispersion correction - `orbitals`: Orbital energies, HOMO/LUMO, gap - `frequencies`: Vibrational frequencies, imaginary modes, IR intensities - `thermochemistry`: ZPE, enthalpy, Gibbs energy, entropy - `all`: Parse everything available

### Step 5: Manual output inspection

For properties not covered by the built-in parser (excited-state energies, NMR shifts, spin populations, natural orbitals, etc.), read the ORCA `calculation.property.txt` file directly.

## 3. Common Use Cases

| Method | Key ORCA Keywords | Notes | |----------------------------|---------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Multi-step SCF convergence | `! GuessMode=CMatrix` | Some SCFs are difficult to converge, solving it multiple steps, converging first on a small basis set and loose criterion and launching it again with the desired parameters | | TD-DFT excited states | `! B3LYP def2-TZVP`, `%tddft NRoots N end` | Use TDA for faster approximation | | CASSCF/NEVPT2 | `! CASSCF def2-TZVP`, `%casscf nel N norb M end` | Active space selection is critical | | DFT + NMR | `! B3LYP def2-TZVP NMR` | Shielding tensors in output | | DFT + EPR | `! B3LYP def2-TZVP EPR/ORP` | g-tensor and hyperfine couplings | | Relativistic (ZORA) | `! B3LYP ZORA def2-TZVP SARC/J` | For heavy elements; use SARC basis sets | | Scan/Relaxed scan | `! B3LYP def2-SVP Opt`, `%geom Scan ... end` | Potential energy surface scans |

## 4. Output Files

- `calculation_results.json`: Summary with energy, SCF convergence, return code, and any input warnings - `<input_stem>.property.txt`: Structured ORCA output file of all properties - `<input_stem>.out`: Full ORCA output file, only suitable for debugging errors - Various ORCA-generated files (`.gbw`, `.densities`, `.engrad`, etc.) in the output directory - `parsed_results.json` (if parser was run): Structured extraction of requested properties

## 5. Constraints

- **Input correctness:** The agent is responsible for writing a valid ORCA input file. The runner performs basic validation but cannot catch all syntax errors, ORCA itself will report those in the output. - **SCF convergence:** Always check that the SCF converged. If it did not, try `SlowConv`, `VerySlowConv`, or adjust `%scf MaxIter` and damping settings. - **Memory:** ORCA can be memory-intensive for correlated methods. Set `%maxcore` appropriately (rule of thumb: total available RAM / nprocs, leaving some for the OS). - **Disk:** Post-HF methods (CCSD(T), CASSCF) can generate large temporary files. Ensure sufficient disk space. - **ORCA binary:** `ORCA_BINARY_PATH` must be set and point to a working ORCA installation. - **Environment:** All commands require the `orca-agent` conda environment. - **Parallelization:** ORCA uses OpenMPI internally. Do not run multiple ORCA instances on overlapping core sets. - **Output parsing:** The built-in parser covers common output patterns. For uncommon methods or output formats, the raw `.out` file must be inspected directly.

## References

- Neese, F., "Software update: The ORCA program system—Version 5.0", *WIREs Comput. Mol. Sci.*, 2022. [DOI](https://doi.org/10.1002/wcms.1606) - ORCA 6.1 Tutorials: [https://www.faccts.de/docs/orca/6.1/tutorials/](https://www.faccts.de/docs/orca/6.1/tutorials/index.html)

---

**Author:** Miguel Steiner **Contact:** [GitHub @steinmig](https://github.com/steinmig)

--- name: chem-dft-orca-advanced-calculation description: Write and run custom ORCA input files for advanced electronic structure methods or settings not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF, NMR/EPR, and more. category: [chemistry] ---

# Advanced ORCA Calculation

## Goal

Enable advanced ORCA quantum chemistry calculations by constructing a custom ORCA input file from scratch. This skill covers methods and features not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF settings, NMR/EPR properties, and more.

> [!IMPORTANT] > For **standard DFT single-point** calculations (energy, gradients, Hessian), use the [singlepoint skill](../chem-dft-orca-singlepoint/SKILL.md) instead. For **geometry optimization**, use the [optimization skill](../chem-dft-orca-optimization/SKILL.md). This skill is for cases where those wrappers do not expose the needed method or settings.

## 1. Prerequisites

- **Conda environment:** `orca-agent` with `ase` installed (SCINE not required for this skill) - **ORCA binary:** The environment variable `ORCA_BINARY_PATH` must point to the ORCA executable ```bash export ORCA_BINARY_PATH=/path/to/orca ``` - **ORCA documentation:** Consult the [ORCA 6.1 tutorials](https://www.faccts.de/docs/orca/6.1/tutorials/index.html) for method-specific input syntax, keyword blocks, and recommended settings

## 2. Workflow

### Step 1: Understand the user's request

Identify the target method, property, and system. Determine which ORCA keywords and blocks are needed. If unsure, consult the tutorials linked above for the specific method.

### Step 2: Write the ORCA input file

Create a `.inp` file following ORCA input syntax. Every input file should include:

**Mandatory elements:** - A keyword line starting with `!` specifying the method, basis set, and job type - A `*xyzfile` entry referencesing an external .xyz file

**Strongly recommended elements:** - `%pal nprocs N end`: parallelization (always set this to avoid single-core runs) - `%maxcore M`: memory per core in MB (e.g. 4000 for 4 GB per core)

**Example — TD-DFT excited states:** ``` ! B3LYP def2-TZVP TightSCF %pal nprocs 4 end %maxcore 4000

%tddft NRoots 10 MaxDim 5 end

* xyzfile 0 1 molecule.xyz ```

**Example: DLPNO-CCSD(T) single point:** ``` ! DLPNO-CCSD(T) def2-TZVPP def2-TZVPP/C TightSCF %pal nprocs 8 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: Geometry optimization with frequency calculation:** ``` ! B3LYP def2-TZVP D3BJ Opt Freq TightSCF %pal nprocs 4 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: CASSCF multi-reference:** ``` ! CASSCF def2-TZVP %pal nprocs 4 end %maxcore 8000

%casscf nel 6 norb 6 nroots 3 end

* xyzfile 0 1 molecule.xyz ```

> [!TIP] > When using an external `.xyz` file with `* xyzfile charge mult filename.xyz`, the `.xyz` file must be placed in the same directory where ORCA runs (the `--output_dir`).

### Step 3: Run the calculation

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/run_orca_input.py \ --input_file calculation.inp \ --output_dir research/my_project/advanced_calc ```

The script will: 1. Validate basic input structure and warn about missing `%pal`/`%maxcore` 2. Copy the input file to the output directory 3. Execute ORCA and capture all output 4. Parse the final electronic energy from the output 5. Save a `calculation_results.json` summary

### Step 4: Parse results

For standard energies, the runner script already extracts the final energy. For other properties, use the dedicated parser:

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/parse_orca_output.py \ --output_file research/my_project/advanced_calc/calculation.out \ --property energy orbitals ```

Available `--property` options in the parser: - `energy`: Final energy, nuclear repulsion, dispersion correction - `orbitals`: Orbital energies, HOMO/LUMO, gap - `frequencies`: Vibrational frequencies, imaginary modes, IR intensities - `thermochemistry`: ZPE, enthalpy, Gibbs energy, entropy - `all`: Parse everything available

### Step 5: Manual output inspection

For properties not covered by the built-in parser (excited-state energies, NMR shifts, spin populations, natural orbitals, etc.), read the ORCA `calculation.property.txt` file directly.

## 3. Common Use Cases

| Method | Key ORCA Keywords | Notes | |----------------------------|---------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Multi-step SCF convergence | `! GuessMode=CMatrix` | Some SCFs are difficult to converge, solving it multiple steps, converging first on a small basis set and loose criterion and launching it again with the desired parameters | | TD-DFT excited states | `! B3LYP def2-TZVP`, `%tddft NRoots N end` | Use TDA for faster approximation | | CASSCF/NEVPT2 | `! CASSCF def2-TZVP`, `%casscf nel N norb M end` | Active space selection is critical | | DFT + NMR | `! B3LYP def2-TZVP NMR` | Shielding tensors in output | | DFT + EPR | `! B3LYP def2-TZVP EPR/ORP` | g-tensor and hyperfine couplings | | Relativistic (ZORA) | `! B3LYP ZORA def2-TZVP SARC/J` | For heavy elements; use SARC basis sets | | Scan/Relaxed scan | `! B3LYP def2-SVP Opt`, `%geom Scan ... end` | Potential energy surface scans |

## 4. Output Files

- `calculation_results.json`: Summary with energy, SCF convergence, return code, and any input warnings - `<input_stem>.property.txt`: Structured ORCA output file of all properties - `<input_stem>.out`: Full ORCA output file, only suitable for debugging errors - Various ORCA-generated files (`.gbw`, `.densities`, `.engrad`, etc.) in the output directory - `parsed_results.json` (if parser was run): Structured extraction of requested properties

## 5. Constraints

- **Input correctness:** The agent is responsible for writing a valid ORCA input file. The runner performs basic validation but cannot catch all syntax errors, ORCA itself will report those in the output. - **SCF convergence:** Always check that the SCF converged. If it did not, try `SlowConv`, `VerySlowConv`, or adjust `%scf MaxIter` and damping settings. - **Memory:** ORCA can be memory-intensive for correlated methods. Set `%maxcore` appropriately (rule of thumb: total available RAM / nprocs, leaving some for the OS). - **Disk:** Post-HF methods (CCSD(T), CASSCF) can generate large temporary files. Ensure sufficient disk space. - **ORCA binary:** `ORCA_BINARY_PATH` must be set and point to a working ORCA installation. - **Environment:** All commands require the `orca-agent` conda environment. - **Parallelization:** ORCA uses OpenMPI internally. Do not run multiple ORCA instances on overlapping core sets. - **Output parsing:** The built-in parser covers common output patterns. For uncommon methods or output formats, the raw `.out` file must be inspected directly.

## References

- Neese, F., "Software update: The ORCA program system—Version 5.0", *WIREs Comput. Mol. Sci.*, 2022. [DOI](https://doi.org/10.1002/wcms.1606) - ORCA 6.1 Tutorials: [https://www.faccts.de/docs/orca/6.1/tutorials/](https://www.faccts.de/docs/orca/6.1/tutorials/index.html)

---

**Author:** Miguel Steiner **Contact:** [GitHub @steinmig](https://github.com/steinmig)

--- name: chem-dft-orca-advanced-calculation description: Write and run custom ORCA input files for advanced electronic structure methods or settings not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF, NMR/EPR, and more. category: [chemistry] ---

# Advanced ORCA Calculation

## Goal

Enable advanced ORCA quantum chemistry calculations by constructing a custom ORCA input file from scratch. This skill covers methods and features not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF settings, NMR/EPR properties, and more.

> [!IMPORTANT] > For **standard DFT single-point** calculations (energy, gradients, Hessian), use the [singlepoint skill](../chem-dft-orca-singlepoint/SKILL.md) instead. For **geometry optimization**, use the [optimization skill](../chem-dft-orca-optimization/SKILL.md). This skill is for cases where those wrappers do not expose the needed method or settings.

## 1. Prerequisites

- **Conda environment:** `orca-agent` with `ase` installed (SCINE not required for this skill) - **ORCA binary:** The environment variable `ORCA_BINARY_PATH` must point to the ORCA executable ```bash export ORCA_BINARY_PATH=/path/to/orca ``` - **ORCA documentation:** Consult the [ORCA 6.1 tutorials](https://www.faccts.de/docs/orca/6.1/tutorials/index.html) for method-specific input syntax, keyword blocks, and recommended settings

## 2. Workflow

### Step 1: Understand the user's request

Identify the target method, property, and system. Determine which ORCA keywords and blocks are needed. If unsure, consult the tutorials linked above for the specific method.

### Step 2: Write the ORCA input file

Create a `.inp` file following ORCA input syntax. Every input file should include:

**Mandatory elements:** - A keyword line starting with `!` specifying the method, basis set, and job type - A `*xyzfile` entry referencesing an external .xyz file

**Strongly recommended elements:** - `%pal nprocs N end`: parallelization (always set this to avoid single-core runs) - `%maxcore M`: memory per core in MB (e.g. 4000 for 4 GB per core)

**Example — TD-DFT excited states:** ``` ! B3LYP def2-TZVP TightSCF %pal nprocs 4 end %maxcore 4000

%tddft NRoots 10 MaxDim 5 end

* xyzfile 0 1 molecule.xyz ```

**Example: DLPNO-CCSD(T) single point:** ``` ! DLPNO-CCSD(T) def2-TZVPP def2-TZVPP/C TightSCF %pal nprocs 8 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: Geometry optimization with frequency calculation:** ``` ! B3LYP def2-TZVP D3BJ Opt Freq TightSCF %pal nprocs 4 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: CASSCF multi-reference:** ``` ! CASSCF def2-TZVP %pal nprocs 4 end %maxcore 8000

%casscf nel 6 norb 6 nroots 3 end

* xyzfile 0 1 molecule.xyz ```

> [!TIP] > When using an external `.xyz` file with `* xyzfile charge mult filename.xyz`, the `.xyz` file must be placed in the same directory where ORCA runs (the `--output_dir`).

### Step 3: Run the calculation

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/run_orca_input.py \ --input_file calculation.inp \ --output_dir research/my_project/advanced_calc ```

The script will: 1. Validate basic input structure and warn about missing `%pal`/`%maxcore` 2. Copy the input file to the output directory 3. Execute ORCA and capture all output 4. Parse the final electronic energy from the output 5. Save a `calculation_results.json` summary

### Step 4: Parse results

For standard energies, the runner script already extracts the final energy. For other properties, use the dedicated parser:

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/parse_orca_output.py \ --output_file research/my_project/advanced_calc/calculation.out \ --property energy orbitals ```

Available `--property` options in the parser: - `energy`: Final energy, nuclear repulsion, dispersion correction - `orbitals`: Orbital energies, HOMO/LUMO, gap - `frequencies`: Vibrational frequencies, imaginary modes, IR intensities - `thermochemistry`: ZPE, enthalpy, Gibbs energy, entropy - `all`: Parse everything available

### Step 5: Manual output inspection

For properties not covered by the built-in parser (excited-state energies, NMR shifts, spin populations, natural orbitals, etc.), read the ORCA `calculation.property.txt` file directly.

## 3. Common Use Cases

| Method | Key ORCA Keywords | Notes | |----------------------------|---------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Multi-step SCF convergence | `! GuessMode=CMatrix` | Some SCFs are difficult to converge, solving it multiple steps, converging first on a small basis set and loose criterion and launching it again with the desired parameters | | TD-DFT excited states | `! B3LYP def2-TZVP`, `%tddft NRoots N end` | Use TDA for faster approximation | | CASSCF/NEVPT2 | `! CASSCF def2-TZVP`, `%casscf nel N norb M end` | Active space selection is critical | | DFT + NMR | `! B3LYP def2-TZVP NMR` | Shielding tensors in output | | DFT + EPR | `! B3LYP def2-TZVP EPR/ORP` | g-tensor and hyperfine couplings | | Relativistic (ZORA) | `! B3LYP ZORA def2-TZVP SARC/J` | For heavy elements; use SARC basis sets | | Scan/Relaxed scan | `! B3LYP def2-SVP Opt`, `%geom Scan ... end` | Potential energy surface scans |

## 4. Output Files

- `calculation_results.json`: Summary with energy, SCF convergence, return code, and any input warnings - `<input_stem>.property.txt`: Structured ORCA output file of all properties - `<input_stem>.out`: Full ORCA output file, only suitable for debugging errors - Various ORCA-generated files (`.gbw`, `.densities`, `.engrad`, etc.) in the output directory - `parsed_results.json` (if parser was run): Structured extraction of requested properties

## 5. Constraints

- **Input correctness:** The agent is responsible for writing a valid ORCA input file. The runner performs basic validation but cannot catch all syntax errors, ORCA itself will report those in the output. - **SCF convergence:** Always check that the SCF converged. If it did not, try `SlowConv`, `VerySlowConv`, or adjust `%scf MaxIter` and damping settings. - **Memory:** ORCA can be memory-intensive for correlated methods. Set `%maxcore` appropriately (rule of thumb: total available RAM / nprocs, leaving some for the OS). - **Disk:** Post-HF methods (CCSD(T), CASSCF) can generate large temporary files. Ensure sufficient disk space. - **ORCA binary:** `ORCA_BINARY_PATH` must be set and point to a working ORCA installation. - **Environment:** All commands require the `orca-agent` conda environment. - **Parallelization:** ORCA uses OpenMPI internally. Do not run multiple ORCA instances on overlapping core sets. - **Output parsing:** The built-in parser covers common output patterns. For uncommon methods or output formats, the raw `.out` file must be inspected directly.

## References

- Neese, F., "Software update: The ORCA program system—Version 5.0", *WIREs Comput. Mol. Sci.*, 2022. [DOI](https://doi.org/10.1002/wcms.1606) - ORCA 6.1 Tutorials: [https://www.faccts.de/docs/orca/6.1/tutorials/](https://www.faccts.de/docs/orca/6.1/tutorials/index.html)

---

**Author:** Miguel Steiner **Contact:** [GitHub @steinmig](https://github.com/steinmig)

--- name: chem-dft-orca-advanced-calculation description: Write and run custom ORCA input files for advanced electronic structure methods or settings not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF, NMR/EPR, and more. category: [chemistry] ---

# Advanced ORCA Calculation

## Goal

Enable advanced ORCA quantum chemistry calculations by constructing a custom ORCA input file from scratch. This skill covers methods and features not available through the SCINE wrapper, including multi-reference methods, excited states, relativistic effects, advanced SCF settings, NMR/EPR properties, and more.

> [!IMPORTANT] > For **standard DFT single-point** calculations (energy, gradients, Hessian), use the [singlepoint skill](../chem-dft-orca-singlepoint/SKILL.md) instead. For **geometry optimization**, use the [optimization skill](../chem-dft-orca-optimization/SKILL.md). This skill is for cases where those wrappers do not expose the needed method or settings.

## 1. Prerequisites

- **Conda environment:** `orca-agent` with `ase` installed (SCINE not required for this skill) - **ORCA binary:** The environment variable `ORCA_BINARY_PATH` must point to the ORCA executable ```bash export ORCA_BINARY_PATH=/path/to/orca ``` - **ORCA documentation:** Consult the [ORCA 6.1 tutorials](https://www.faccts.de/docs/orca/6.1/tutorials/index.html) for method-specific input syntax, keyword blocks, and recommended settings

## 2. Workflow

### Step 1: Understand the user's request

Identify the target method, property, and system. Determine which ORCA keywords and blocks are needed. If unsure, consult the tutorials linked above for the specific method.

### Step 2: Write the ORCA input file

Create a `.inp` file following ORCA input syntax. Every input file should include:

**Mandatory elements:** - A keyword line starting with `!` specifying the method, basis set, and job type - A `*xyzfile` entry referencesing an external .xyz file

**Strongly recommended elements:** - `%pal nprocs N end`: parallelization (always set this to avoid single-core runs) - `%maxcore M`: memory per core in MB (e.g. 4000 for 4 GB per core)

**Example — TD-DFT excited states:** ``` ! B3LYP def2-TZVP TightSCF %pal nprocs 4 end %maxcore 4000

%tddft NRoots 10 MaxDim 5 end

* xyzfile 0 1 molecule.xyz ```

**Example: DLPNO-CCSD(T) single point:** ``` ! DLPNO-CCSD(T) def2-TZVPP def2-TZVPP/C TightSCF %pal nprocs 8 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: Geometry optimization with frequency calculation:** ``` ! B3LYP def2-TZVP D3BJ Opt Freq TightSCF %pal nprocs 4 end %maxcore 4000

* xyzfile 0 1 molecule.xyz ```

**Example: CASSCF multi-reference:** ``` ! CASSCF def2-TZVP %pal nprocs 4 end %maxcore 8000

%casscf nel 6 norb 6 nroots 3 end

* xyzfile 0 1 molecule.xyz ```

> [!TIP] > When using an external `.xyz` file with `* xyzfile charge mult filename.xyz`, the `.xyz` file must be placed in the same directory where ORCA runs (the `--output_dir`).

### Step 3: Run the calculation

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/run_orca_input.py \ --input_file calculation.inp \ --output_dir research/my_project/advanced_calc ```

The script will: 1. Validate basic input structure and warn about missing `%pal`/`%maxcore` 2. Copy the input file to the output directory 3. Execute ORCA and capture all output 4. Parse the final electronic energy from the output 5. Save a `calculation_results.json` summary

### Step 4: Parse results

For standard energies, the runner script already extracts the final energy. For other properties, use the dedicated parser:

```bash # Env: orca-agent python .agent/skills/chem-dft-orca-advanced-calculation/scripts/parse_orca_output.py \ --output_file research/my_project/advanced_calc/calculation.out \ --property energy orbitals ```

Available `--property` options in the parser: - `energy`: Final energy, nuclear repulsion, dispersion correction - `orbitals`: Orbital energies, HOMO/LUMO, gap - `frequencies`: Vibrational frequencies, imaginary modes, IR intensities - `thermochemistry`: ZPE, enthalpy, Gibbs energy, entropy - `all`: Parse everything available

### Step 5: Manual output inspection

For properties not covered by the built-in parser (excited-state energies, NMR shifts, spin populations, natural orbitals, etc.), read the ORCA `calculation.property.txt` file directly.

## 3. Common Use Cases

| Method | Key ORCA Keywords | Notes | |----------------------------|---------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Multi-step SCF convergence | `! GuessMode=CMatrix` | Some SCFs are difficult to converge, solving it multiple steps, converging first on a small basis set and loose criterion and launching it again with the desired parameters | | TD-DFT excited states | `! B3LYP def2-TZVP`, `%tddft NRoots N end` | Use TDA for faster approximation | | CASSCF/NEVPT2 | `! CASSCF def2-TZVP`, `%casscf nel N norb M end` | Active space selection is critical | | DFT + NMR | `! B3LYP def2-TZVP NMR` | Shielding tensors in output | | DFT + EPR | `! B3LYP def2-TZVP EPR/ORP` | g-tensor and hyperfine couplings | | Relativistic (ZORA) | `! B3LYP ZORA def2-TZVP SARC/J` | For heavy elements; use SARC basis sets | | Scan/Relaxed scan | `! B3LYP def2-SVP Opt`, `%geom Scan ... end` | Potential energy surface scans |

## 4. Output Files

- `calculation_results.json`: Summary with energy, SCF convergence, return code, and any input warnings - `<input_stem>.property.txt`: Structured ORCA output file of all properties - `<input_stem>.out`: Full ORCA output file, only suitable for debugging errors - Various ORCA-generated files (`.gbw`, `.densities`, `.engrad`, etc.) in the output directory - `parsed_results.json` (if parser was run): Structured extraction of requested properties

## 5. Constraints

- **Input correctness:** The agent is responsible for writing a valid ORCA input file. The runner performs basic validation but cannot catch all syntax errors, ORCA itself will report those in the output. - **SCF convergence:** Always check that the SCF converged. If it did not, try `SlowConv`, `VerySlowConv`, or adjust `%scf MaxIter` and damping settings. - **Memory:** ORCA can be memory-intensive for correlated methods. Set `%maxcore` appropriately (rule of thumb: total available RAM / nprocs, leaving some for the OS). - **Disk:** Post-HF methods (CCSD(T), CASSCF) can generate large temporary files. Ensure sufficient disk space. - **ORCA binary:** `ORCA_BINARY_PATH` must be set and point to a working ORCA installation. - **Environment:** All commands require the `orca-agent` conda environment. - **Parallelization:** ORCA uses OpenMPI internally. Do not run multiple ORCA instances on overlapping core sets. - **Output parsing:** The built-in parser covers common output patterns. For uncommon methods or output formats, the raw `.out` file must be inspected directly.

## References

- Neese, F., "Software update: The ORCA program system—Version 5.0", *WIREs Comput. Mol. Sci.*, 2022. [DOI](https://doi.org/10.1002/wcms.1606) - ORCA 6.1 Tutorials: [https://www.faccts.de/docs/orca/6.1/tutorials/](https://www.faccts.de/docs/orca/6.1/tutorials/index.html)

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**Author:** Miguel Steiner **Contact:** [GitHub @steinmig](https://github.com/steinmig)