Grant permission to group to spList, change inherit -> unique, change other library permissions using POWERSHELL

I understand that you want to grant permission for  the owners group to the Audit Logs library. You can use the script below:

$ownersSPGroupName = "owners"

$webUrl="http://serverURL"

$spweb = Get-SPWeb $webUrl

# Look up the list named "Audit Logs"

$questionsList = $spWeb.Lists["Audit Logs "]

# Set the Read access Item-level permissions settings to "Read items that were created by the user"

$questionsList.ReadSecurity = 2

# Set the Create and Edit access Item-level permissions to "Create items and edit items that were created by the user

$questionsList.WriteSecurity = 2

# Assign the "Contribute" RoleDefition to the site's owners group

$ownersSPGroup = $spWeb.Groups[$ownersSPGroupName]

$questionsList.BreakRoleInheritance($true)

$assignment = New-Object Microsoft.SharePoint.SPRoleAssignment($ownersSPGroup)

# Assuming this is a default site, we'll look for a role definition of the type "Contributer".

# This way, the script will also work with SharePoint sites created in languages besides English.

$assignment.RoleDefinitionBindings.Add(($spWeb.RoleDefinitions | Where-Object { $_.Type -eq "Contributor" }))

$questionsList.RoleAssignments.Add($assignment)

$questionsList.Update()

$spWeb.Dispose()

$spSite.Dispose()

For more information, please refer to this site:

Modifying list permissions from Powershell: http://blog.morg.nl/2011/09/modifying-list-permissions-from-powershell/

Adding permission to list using powershell: http://social.technet.microsoft.com/forums/en-US/sharepointadminprevious/thread/4373cef1-2471-4199-aa16-784684fc82de