Function build_gaussian_header_internal 

fn build_gaussian_header_internal(
    config: &Config,
    charge: i32,
    mult: usize,
    td: &str,
) -> String

Internal Gaussian header builder that doesn’t modify the method string.

This function constructs the route section and title card for a Gaussian input file based on the provided configuration and state-specific parameters. It assumes the method string has already been modified by modify_method_for_run_mode().

Arguments

• config - The global configuration with pre-modified method string
• charge - Molecular charge for the current state
• mult - Spin multiplicity for the current state
• td - TD-DFT keywords (e.g., “TD(NStates=5,Root=1)”), may contain comments

Returns

Returns a String containing the formatted Gaussian input header.