@article{Zhang_2006 author = {Hongwu Zhang and Q. Gao and Wanxie Zhong}, title = {Variational Principle and Mechanical Computation for Energy Bands of Periodic Materials}, journal = {International Journal for Multiscale Computational Engineering}, issn = {1543-1649}, year = {2006}, volume = {4}, number = {1}, pages = {3--18} }