Legal Question in Real Estate Law in California

You don't need terms in the lease. By law you are entitled to collect rent from them until you get the property re-rented, provided you take all commercially reasonable steps to re-rent it as promptly as possible, and the costs of any work you need to have done to prepare it to rent, along with advertising expenses, etc. Basically whatever it reasonably costs you to get a new tenant in. You can't have unnecessary work done, or waste money and then charge them, but all reasonable costs should be recoverable.

I agree. Indeed, a specific penalty for breach written into a lease would likely be invalid. You are entitled to your actual losses which you sustain despite making a reasonable effort to re-rent the place and cut your losses, and the losses would be the sum of lost rents, cleaning and repair costs, and re-renting expenses such as advertising and screening applicants. If these losses end up exceeding the deposit, you can bill the departed tenants for the shortfall, and if they don't pay, you can sue. If there is a balance in their favor, it must be refunded. Since you are new to the landlording business, I suggest you acquire and study a paperback self-help law book on the subject of landlord-tenant rights or how to be a successful California landlord.