Function build_gaussian_header 

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

Builds a Gaussian input file header string (legacy interface).

This function is maintained for backward compatibility. New code should use build_program_header() which includes dynamic method modification.

Arguments

• config - The global configuration for the MECP calculation
• 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 with clean route section.