Qualitative intruder-state problems in effective Hamiltonian theory and their solution through intermediate Hamiltonians.  [electronic resource] 

 -  Physical review. A, General physics  Jun 1987 
 - 4930-4941 p.  digital 
<br/><br/> Publication Type: Journal Article 
<br/><br/><label>ISSN: </label>0556-2791 
<br/><br/><label>Standard No.: </label>10.1103/physreva.35.4930  doi