Translate Chapter 4 (Methods for determining electronic structure) to English

[Copilot]

Translates Chapter 4 "Metody wyznaczania struktury elektronowej" (Methods for determining electronic structure) from Polish to English, continuing the translation series started in PRs #26 (Chapter 1), #30 (Chapter 2), and #31 (Chapter 3).

Sections Translated

• 4.1 General characteristics - Overview of three main computational method categories (pseudopotentials, localized orbitals, augmented waves)
• 4.2 Pseudopotentials - Norm-conserving, ultrasoft (Vanderbilt), and PAW methods
• 4.3 Localized orbitals - Tight-binding, Wannier functions, Gaussian functions (LCAO)
• 4.4 Augmented waves and atomic spheres - KKR, LAPW/APW+LO, and LMTO/ASA methods

Technical Notes

• All mathematical equations, citations, and cross-references preserved
• Figure captions translated
• Terminology consistent with previous chapter translations
• LaTeX structure maintained throughout

Branch based on book to avoid conflicts with ongoing work.

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