Are multi-megaton antimatter induced fusion explosions theoretically possible? I just finished reading  this research about antimatter induced fusion and thermonuclear reactions. 
And one conclusion I could make is that very little mass of antimatter (in range of micrograms) is needed to initiate a fusion reaction in lithium-deuteride fuel.
Also, in page 14 in this PDF file, there is a theoretical design of a 1-kiloton antimatter induced fusion bomb.
Now, I actually have 2 questions.
Firstly, 100 grams of lithium-deuteride is used in this theoretical 1 kt design. But according to this, 100 grams of lithium-deuteride should yield 6.4 kilotons not only 1 kiloton, so is there any explanation of this ?
Secondly, since I seem to find only low yield designs of antimatter induced/catalyzed fusion bombs, a doubt about the feasibility of larger yield came to my mind. So, if a single kiloton fusion reaction is feasible with a certain amount of antimatter, then should we consider fusing more fuel with even more antimatter feasible too ?
Note : I completely understand the difficulty of making, handling and storing antimatter, and I am not saying this thing is going to be made any time soon. I am just curious about the physics part behind it.
 A: Aside: What's with this obsession with multimegaton explosions? End aside.
There are no inherent limits on the size of fusion explosion. Moreover, with the use of staged weapon design, antimatter amount needed to initiate the arbitrary powerful explosion would essentially remain the same.
Ordinary fusion explosion (Teller-Ulam design) is initiated by the x-rays released by fission primary that compress the secondary fusion fuel that is simultaneously heated with fissile sparkplug.
If we try to eliminate the fission, while already having the antimatter initiated small scale fusion device, the obvious way would be to use this device as primary to compress and heat the secondary fusion fuel dose. 
Note, that since we also want to eliminate uranium sparkplug we need to provide mechanisms to not only compress but also heat the deuterium-tritium of the secondary. And the energy needed for such heating needed to be extracted from the primary explosion. This means that the hohlraum needs to be somewhat redesigned.
This secondary explosion could then be used to initiate the explosion of the third fusion stage.
In Tsar bomba ~1 megaton fission primary is enough to initiate 56 megaton fusion secondary. So using the value 50 for increase in yield between stages and using as primary the device mentioned in the question we can estimate the following yield for three stages:
primary ~ 1 kiloton yield,  secondary ~ 50 kiloton yield, tertiary ~ 2.5 megaton.
