electron density functional method graphene pseudopotential method графен метод псевдопотенцiалу метод функцiонала електронної густини - Hetero- and low-dimensional structures ab initio calculations ab initio pseudopotential activation bending compression density functional theory electron density functiona electron density functional first-principle calculations graphene nanoribbons heterocomposites mechanical compression metallic clusters methanol nanocatalysts nanocellulose piezoelectric effects polymer (L-lactic acid) pseudopotential twisting water активацiя